To an extent you can say that. But that isn't necessarily true. I think you should read that more as 'ability to achieve more' with a simplistic design approach. And in order to be simple you will have to divide the task into easily understandable and easy to assemble parts. The UNIX philosophy to be frank with you,can be explain with the following example.
All programming is some sort of data manipulation! And in some cases programming is also program manipulation itself(Meta programming). Now the way UNIX philosophy works is, Imagine processing text. What is text? Text is some sort of data after all. When assemble into organized definition Text also becomes XML's and JSON's. Text can also be a list of numbers, Text can also be csv's, tsv's and what not! In other Text or string can represent a real huge area of programming data, just because its context can twisted and turned into what we want!
All programming requires data organization of some sort. Organizing requires searching...
a. There you go with just have 'grep', 'fgrep' and its family to do that.
Once you search you need to do some sorting..
b. Now we have 'sort' command to do that.
You've just sorted two files, now you wish to compare them.
c. Now we have 'diff', 'cmp' et al to do that.
You've just found there is no difference between the files. You need more of organized data now.
d. You have 'cat', pipes and redirection operators to write to a file.
You need more specific parsing..
e. You have head, tail, more, less, cut et al to do that...
All of this sew together using the '|' to generate real powerful stuff some time without writing any code at all. For more searching and sewing you have..
f. awk, shell and sed.
awk, shell and sed give you more control over text than what cut, diff et al can give you. Have you ever wondered that command1 | command2 | command3 ... series is a sort of workflow mechanism. When combined with If's this becomes more powerful.
Now comes more fun.
Have you ever heard of a utility called 'Perl', this thing is so powerful you can virtually do any task at hand with as little work imaginable. Sewed together with a utility like DBM you can do even small time persistence demands for your application. Remember we haven't even stepped out of the text world but yet managed to cover most aspects of a programming environment.
So I think UNIX is more than a operating system. It's a collection of tools and environment designed to solve the problems in the most simple way. A simple way doesn't necessarily imply simplicity of implementation of the solution. But simplicity itself doesn't take you much far.
I read this some where on reddit.
"If your only design goal is simplicity, you will get as many users as Plan9"