quality control?

I've just got through my third MSI Geforce card in 18 months --
luckily the PC's still under guarantee so I'm not the one losing
out, apart from a few days' inconvenience. But I find myself
wondering what's the reason; I've never had that kind of component
failure before. They've each died of different things -- with the
original one (a GF3) the fan seized up, and evesham.com who supplied
the PC replaced it with a GF4 Ti4200 (nice, to get something better
than you paid for). That started getting colour corruption and
crashing with increasing regularity; I seem to remember the engineer
saying the memory on it had gone. So he put another one of the same
model on, and a couple of days ago, with no warning (about an hour
after I was last using it), it completely died on me: wouldn't boot
up, giving me a screenful of multicoloured square blotches, followed
after a few seconds' think by a screenful of multicoloured vertical
lines. Then the system would think for a bit, power down, try to
reboot, and repeat ad infinitum. I tried out an old GF1 that I've
been using in my old PC for about three years I guess, and it's
fine. So the engineer is on his way again.
So, I ask myself (and you lot out there, obviously): what's up
with that? Am I just unlucky? Is the quality control just not good
enough? Or is it possible that there's some subtle, marginal fault
somewhere else in the system that's putting stress on the graphics
cards and causing them to die of premature old age? Obviously the
first one, with the fan, must have just been a mechanical fault, but
with the other two I'm starting to get quite neurotic. I wouldn't
have the first clue where to look for a trigger or underlying
condition. I don't think I'm abusing it -- I've never overclocked
and the system doesn't stay on for days on end or spend *that* much
of its time playing games. Any thoughts, at all?

jd