You would only be punishing yourself by switching OS platforms just because an update wasn't announced today. You're going to go out and buy all new software for the PC, change your workflow, network setup, and backup strategy just to protest Apple not releasing new iMac hardware today?
Unless all you do on your iMac is check your e-mail and surf the internet, changing OS platforms is going to be a big investment in terms of both time and money.
Today wasn't the only day all year Apple could announce a new iMac. The iMac will be updated, just not today.
You can certainly switch to a PC if you want - no one's stopping you - but it still seems to me as rather drastic.