The place I work for is the same. In that sort of large company you would normally have some sort a relationship with a computer repairs company and that company would accept a purchase order. Yes, your company ends up paying $50 or $80 instead of just $12 for the fan and shipping, but it keeps the accountants happy.
Yes it would seem to be the same in most large companies. It is the very people who should know better and be keeping an eye on budgetry spending that cause this issue in the first place.