Sort of like a little bike with training wheels and streamers coming out the ends of the handlebars compared to something like this:

http://www.trekbikes.com/us/en/bikes/mountain_hardtail/9_ser...

Emacs is open source, but so scriptable that I don't think I've ever talked with anyone who's ever delved into the C code. Textmate, on the other hand, is not open source, and so you depend entirely on the author to provide you with timely updates and features. It may be scriptable to some degree, but if you want to do something more with it, you simply can't.