Apart from the sure smell of sarcasm in this thread I'd would also like to mention that other factors are included too.
The brand is often not that relevant except if your looking to buy a compact computer; but the rest is very much the same.
Do take not that maintenance and how you take care of you computer plays a very big role here.
How is the electricity in your area - do you need an Uninterruptable Power Supply to level out some of the spikes & dips in the electricity of your area.
The Room where you store the PC; are there factors that could affect the PC's lifetime such as too much dust; to much vibration the desk the PC is on or maybe a Drying Machine which releases a lot of damp into the air in that area.
Often times the height of your PC also affects its lifetime. Never leave the PC on the floor; there is alot of dust there and could create problems.
The faster the PC the more cool air it needs so you might need to get a good heat sync to ensure tha the PC stays cool. Same as cars; if they're not ventilated the stop working.
Oh yeah, and to do my bit on the sarcasm - remember no PC works without the magic smoke, cause if that smoke comes out; it aint working anylonger. lol
Hope the information was useful for you!!!!