My first MX pants were the MSR World TOur (MSR's lowest level, purchased last Sept). Belt pulled out of pants after about 8 rides. I rivited it back on and still use them. But, both my Children both have had World Tour for years, and no problems (and Cam wore his almost daily for 2+ years).
Cam now has MSR System X (since last XMAS). Those Sys X pants have large rubber piece thats part of the belt, that is rivited to the pants. The Sys X stuff seems to be very well made (comparable to top end FOX IMO, Wife has 360 only, and I have the 360 vented pants) and has so far held up great. I would not hesitate to buy MSR System X again.