99% of the time it is heat that's the killer which leads to blown caps on the transistors. 99% of them I come across are on motherboards but some are in PSU's (Power supplies rarely "burn out" they either die initially or last forever). Video cards also go too but that's because their fans & air ducting can be bad (or the card was used in a cheap chassis) and they overheat or the fans get clogged.
http://andysworld.org.uk/blog/wp-content/uploads/2011/09/psu1.jpg
That's a pic that came up on Google but if you type "blown transistor cap" into Google Images you'll get the picture.
Dell & HP got it right with their workstations - they are far superior to others. If you look at either brand of chassis you will see that they are wide open up front - so things like cat/dog hair or office dirt & dust don't clog up the intake. They also use server grade parts or uber-high end parts where possible - but there is a difference between true server grade parts and workstation parts. Yes they are both high-end but server grade parts are made for environmentally controlled environments which have everything from sound deadening to temperature and humidity control.
I learned the hard way in the beginning with server hardware. It's loud as heck and also very temperamental - the fans got clogged right away and the heat started cooking the chassis. Since most server rooms are dust free and have air conditioning they assume that's where a server will live. On the contrary Dell & HP assume that a Workstation may be used as a server or any other number of grueling 24/7/365 tasks - but at a construction site, on set at a movie, on an oil rig, etc...
The reason why the older high-end workstations are so great is that they are built very robust and 99% of the time they just sit in an office like any other desktop would.
