> Any thoughts on what this could be?
> At this point I'm entertaining the following notions:
> 1) short circuit in the ethernet cable from router to modem?
> 2) wireless router is failing?
> 3) wireless card is failing?

It's option 3, but probably not a hardware failure. Driver and/or
configuration.

The common element here is going into standby, right? There are lots of
cards and their drivers that have had great trouble with coming out of
standby mode.

Do this, when it's working pull up a CMD prompt and type "ipconfig /all" and
note the information it shows you. Put the laptop into standby, move to the
other location and type ipconfig /all again. See what (if anything) is
different. Then type "ipconfig /release" followed by "ipconfig /renew".
This will release/renew the DHCP networking information. Then use ipconfig
/all to show it again. See what's different.

I'm guessing it has everything to do with your laptop going to sleep and not
reconnecting properly on waking back up.