To add to that, AFAIK, Win 8 uses the same drivers as 7, which are basically the same as Vista, so it's like the Win2000 to XP migration, where the driver model remained unchanged, giving kind of a false impression of a lack of drivers.
For the OP: I know it's easy to do armchair quarterbacking, but given support for XP is about to come to an abrupt end within about a years time, I would just save the money of the Windows 7 licenses and just turn around and invest that in a new set of computers once the current set has been paid for. Then you can keep the old ones around for a time, so you aren't in a mad rush to migrate data, etc, and you can give people some time to acclimate to Windows 8 because it will be a pretty big culture shock coming from XP. Some might consider that to be an understatement.
If the current units came with XP, then the hardware is probably pretty old, and it'd be time to consider upgrading. Then the company can happily rediscover it's neo-luddite ways and just sit with Windows 8 for many years to come, because it'll probably be around 2017 before MS drops all support for Win 8. Of course from a business perspective, it's a good idea to not let yourself get too far behind, otherwise you end up having issues with migrating data or getting sticker shock from having to pay full price for some new version of a vital program, the older version you have no longer working on the new OS release. You don't have to upgrade the instant something comes out, but you should try and keep within 1-2 versions of the latest as much as possible. Also have contingency plans in place for what happens if that program vendor goes under, or makes some kind of change that renders it unusable for your company, that sort of thing.