That definitely sounds nightmarish. I'm betting they don't even consult corporate for machines.
90 sites sounds like a bit of a nightmare in its own right. We've got 4 sites and 3 of us in our department (granted, 3 of the sites are 24/7 sites and the 4th site is corporate, and we cover far more than just our ~200 PCs), and even with all our infrastructure in place, that can be crazy. If you had any clout, you could probably force those sites to comply to corporate's rules, but I doubt IT has any teeth in your organization.
Absolutely it's a nightmare, we have a 'minimum spec' that the stores have to buy, but they are the only restrictions, and, up until recently, the policy wasn't enforced! Many of the machines are still using XP, thankfully next month; we are getting over 200 i3's in to replace the outdated machines. Which will make my life easier in the long run, but it's going to be tough going setting them all up :)