You can if it's a user error/maintenance issue, however not saying that that's what happened here. Remember all the issues Kyle had with his yz125? I think he ended up rebuilding it 3 times in the time it only should've needed one. It ended up being a jetting issue aka user error, not a manufacturing defect.
Sorry this isn't a thread about the yz125 being the same bike since what 2000?
There are improvements every year, some bigger than others. For example the addition of DFI in the 2011 model and the dual fuel injection for 2012. Same with the upgrades to the suspension (SFF).
I'd say that one of the most impressive improvements that bikes have had over the years is horsepower/torque (for being the same cc) and suspension. According to MXA's dyno tests on the kx250f:
2008 kx250f - 35 horsepower
2009 kx250f - 35.45 horsepower
2010 kx250f - 36.48 horsepower
2011 kx250f - 37.30 horsepower (DFI was added)
2012 kx250f - 39.55 horsepower (Dual fuel injection added)
2013 kx250f - 41.16 horsepower
With that said, yes most bikes don't have massive changes every year, if it's not broken why change it?