"I guess what I wanted to ask, just for discussion sake, is why S&W over let's say, Glock, Springfield, Sig Sauer, Walther?"
I'll run it down for you:
1. M&P has better egros (for me) than the Glock.
2. M&P cost less than all of the others.
3. M&P fits my hand better than all the others except for Walther, but that mag release on my Gen 1 P99 turned me off.
4. M&P was highly recommended by everyone I knew that owned one.
5. Each of the above has had "teething" issues, but M&P had the least and fixed them the fastest.
6. Just as many aftermarket goodies as Glock.
7. Purpose of Use. Its a duty gun and my CCW. Since it bears very similar size characterisics to my 1911 Commander but without the weight.
8. To your question about why .9mm? Why not? Its been doing the job for over 100 years and the M&P gives me 17+1 to do it. Oh, and I have the .45 too.
9. Warranty (haven't needed it) and CUSTOMER SERVICE.
10. MADE IN THE USA!