Good question. First of all congratulations on your hard work ethic, and your energy for building a career and doing great work - it's a very admirable trait that will take you a long way.
I think a lot of the answers here are off the mark - people are assuming that the original poster is mistaken in his interpretation of his colleagues' behaviour. This leads to lots of replies such as "Effort and Productivity Do Not Equal Effectiveness". In this case, I prefer to take him at this word, that yes his colleagues don't perform as well as he does (as evidenced through bug tracker or simple observation whatever) - let's just assume it's true. Now, how do you answer his question: is it "normal" to not work? My interpretation of what the OP is asking is: "is it normal to work less hard than he does"? Note that he says he is 100% sure they could also do the work in the time he does, if they applied themselves - so he's not claiming superior ability.
My take on this is that it actually is normal behaviour for some people to slack, as it is equally normal behaviour for others to work to the max of their abilities - there's a spectrum. To the OP, clearly you are not one of the former, you are near the latter end of the spectrum. What positions us on a particular point on the spectrum? And can people move along this spectrum? My answers to these 2 questions are: 1) motivation and 2) yes they can move (I've done it myself). JB King's answer addresses this issue of motivation. If you are now in a more senior role in the company, then you can now to some extent guide people's motivation. Whether you use a carrot or a stick is up to you - my sense is that you are more familiar with the stick (correct me if I am wrong).
Your second question is: will you "become like them". Probably not given that you are clearly quite a distance along the slacker spectrum from where they are, but the reality is that, as humans we are strongly influenced by our environments, so you won't be immune to your colleagues. So if you stay in that particular work place for long enough, you may find yourself moving along that motivation spectrum just through the sheer inertia of the place. In the opposite case, if you had, say, joined a startup chasing an IPO back in 1999, you probably would have found not enough hours in the day to get your work done, and you may have found yourself going even further along towards the other end of the spectrum (plus you may have coincidentally noticed your health deteriorating :-) ).
A few personal comments that came to mind reading the question (note these may be of little interest if you are just seeking an answer to your question):
First, my immediate reaction to your question was one of anger. When I paused to consider why, I realised in a moment of shame, that you were essentially reminding me of a younger version of myself. The reason I say shame, is that I was an arrogant son-of-a-bitch, who worked hard, thought I knew it all, and judged all my colleagues harshly for what I perceived to be their slacker attitudes. In fact I judged some of them so harshly that I never allowed myself the opportunity to get to know them as people, and to learn what they could teach me (not just technically but as humans). It was a painful journey for me to allow myself to be part of a "team", each one playing his part - some the generals and some the foot soldiers. Yes it was true that some of them were slackers, but my judgemental attitude prevented me from either understanding them or possibly even motivating them. My bad. So yes, reading your question brought up my anger, but not anger with you, but with my own earlier lack of empathy.
This lack of empathy is quite a common thing among smart technical people - while I don't think techies have more sociopath tendencies than the norm, I certainly have seen enough techies who lack social skills (either learned or through natural empathy) to know it's an issue in the tech world. For example, I wonder did you ever ask yourself what the effect of your actions were on the people who got fired? On their wives, kids, mental health? Did you even know them as people?
What was helpful for me was to focus on improving myself, leading by example, and stop JUDGING other people. It makes people like you a lot more for it, and everyone will be happier.
Finally, it's also an age thing - when I was your age (a year out of college, I guess that makes you 22?) I knew NOTHING. Ironically the younger you are, the more you think you know. One of the great gifts of aging is the realisation that you the more you know, the more there is to know, so in fact, the less you know in relative terms. This leads to a surrendering of control, to try to be less autonomous, to connect more with others so that we can share our skills for the good of everybody (in a quid pro quo manner, NOT in a communist manner LOL). It's normal healthy maturing stuff. If you're already connected to other people (in the REAL world, not in IRC) that will help with that process. It's a bit like the analogy of the more a stone gets rubbed, the more polished it becomes - it's the same with our egos.