The only reason this is difficult...
...is because some businesses (both through management and IT depts) seem to take an ideological approach instead of a practical approach to "THE standard PC". "I am THE ONE true standard PC, thou shalt have no other PC but me" and all that...
Blowing this up into a 'major business dilemma' is frankly pathetic. The question is exactly the same whether you're talking about computers, stationery, desk chairs, salesforce promotional gifts or surgical procedure packs. It's not an "IT" question, it's a "basic administrative principles" question. The question is how high you set the bar that people have to clear before their needs for something non-standard are acted on. And yes, unless you have a workforce you can trust absolutely to only make fully informed, reasonable requests, you do need a bar. An applied mathematics PhD canditate friend of mine once requested his dept to purchase a new SGI workstation for him - when asked "why?" he replied "so I can play Doom at a higher level" - they _thought_ he was joking [this was the early '90s].
This is reasonably well handled in my workplace of 5000+ PCs (Govt health dept of all places). The standard, supported config is broadly based and includes things like WM player and flash, so it exceeds the (legitimate business) needs of the vast white collar majority. The vast majority of users work on a standard PC, standard image, locked down profile with no admin rights, and are fully supported by IT.
Users who have software or hardware needs which aren't met by the standard PC are treated as exceptions, and come under a different support model.
Those of us who can work on standard hardware but need administrator rights get local admin access. Our PC's are supported as far as hardware and standard apps, but if through our local admin we screw something up, the support model is "we will re-image your PC (and install any site-licensed software that's not part of the base image) but the rest is up to you".
Users with non-standard hardware requirements (e.g. techs, medical diagnostics) purchase their hardware through diffferent channels, and get their hardware support through those same channels instead of in house. Depending on the config required, those machines may be quarantined from the domain, and may or may not have the standard application suite installed.