I'm guessing a little on the slide mass but the .22 is a lot lower energy than the center fire rounds and .22's typically have what I would call 1/2 slides. Most of the full size guns like this use aluminum alloy slides to keep the weight down along with lighter recoil springs. I don't know that I'd call it a major factor but I believe it has to play a role. I don't think it's an issue with reliability ect, it just means weaker ammo won't cycle them reliably. Good points from qwiksdraw as the Blazer I planned to use are coated lead.
I bought mine as a full size platform to shoot the cheaper .22 on (and quieter for less neighbor irritation). So the way I look at it, even if I shoot the Super-X SS at $5.50 per 100, that's still way less than .45auto and even way less than 9mm and I get to shoot a full size service style pistol.
For what it's worth, the other .22 I was looking at was the M&P 15-22. That one gets great reviews. Very similar to the regular M&P but with an aluminum slide (a very nice quality slide though). But I wanted a 1911 and I didn't need another .45 auto (too expensive) and the Sig really caught my eye. It's like it was calling to me.
I hope I made the right choice (or I'll probably end up with both eventually).