Yep they do look super similar which is why we cant easily get them in. Other wise we wouldnt have crappy can soft guns with smoked lowers.
Check this thread out if you want some cool ideas for STI builds. You will see the so called pimped out 1911s and the STI's with the polymer grips.
http://www.1911forum.com/forums/show...=75576&page=31
My favorite is the limcat in post 766.