Well, as the 'new guy' let me throw my two bones into the mix...
By a GOOD case from a decent manufacturer, if it has a PSU, it will run for years under 'normal' useage.
By a GOOD case from a decent manufacturer, if it doesn't have a PSU buy a good one. It will also run for years under normal use.
Now, if you are always playing with you PC, overclocking, running raid setups with 5 hardrives, looking into SLI video cards, and a host of other 'hobbiest' type exploits, then by all means buy a $250 dollar PSU and a $300 Titanium case with a Platinum face plate.
However, if you are going to build a machine with typical components (one or two drives, a basic video card, and one or two fans...) most quality built PSUs 350W or so will be fine for years to come.
The idea that faulty PSUs kill more PCs than any thing else, just hasn't been my experience at all in over ten years of rolling my own. They literally just keep going and going, some of them on PSUs that were used when I built them using throw away Aopen cases from where I work. Many times, we are talking about old-school 235w units to boot.
I build my PCs to use them. I only open them up if I have to or if I'm upgrading. Several of them run 24/7 and have been for the last year (minimum). I do heavy photo editing currently, and heavy online gaming previously. Never had a problem with my machines and the 'best' psu I have is an Enermax 350w unit in a machine that's been off-line for a year. My current Antec 350w unit is a year old and still purring like a kitten.
FWIW-I don't have any windows in any of my boxes either....