To me, personally, it is not the possibility to learn technical stuff which would lure me to a startup (technologies come and go - after a couple (dozen), one may not get so excited anymore about the latest and greatest new fad). Rather the chance to make a visible difference in the world, or at least in a community.
In a big corporation, however good place it is, this is almost impossible. In a small startup - at least I imagine so - one can make a difference.
May be it's just me - feel free to call me a naive dreamer :-)