In additon to the above, there's really no reason to reboot when this happens. Just open the Device Manager and do a disable/enable on the wireless NIC. That should bring it back to life.
This is an ongoing issue ever since computers gained the ability to standby/sleep. Some hardware just doesn't wake up properly.
Actually, that's the strange part: trying to troubleshoot the problems via Windows actually does reset. It still takes an actual full reboot to really get back connectivity.