Where are you coming up with this? I've owned an XDm before. Out of all the rounds I shot through it, it had 1 failure to eject due to an underpowered load. From what I've read, that's most other people's experiences as well. I only own the XDs currently from Springfield, but have never had an issue with the XD line of pistols in terms of reliability.

The M&P, Glock, and XD line of pistols all have "defects" that have risen over the years. It's going to happen in any mass-produced firearm, as these aren't handmade customs. Just because I've read someone online posting about how their Glock blew up, their M&P can't hit a barn, or their XD won't feed a round, doesn't mean I buy any of it. These are isolated cases, and as said before these are mass produced firearms that are going to have a margin of defect inherent in their production.

I think you're making a very broad statement with no factual basis. Glocks and M&Ps probably are selected and used more in shooting events, but I strongly doubt it's because of reliability. It probably has to do with initial cost of the firearm (XD line is typically more expensive), aftermarket support, and ergonomic preference.