P.S. To be fair, fear of theft *is* what keeps me from actually riding my bike to the grocery store. Not to work though, but if I worked in a moderate to high crime area (like downtown) and had to leave my bike outside it would be a different story.

I never said anything about putting panniers on the bike, though I would if I did any touring. It's my experience that a rear rack with a bag on top of the rack is the most efficient way to carry a few basic necessities like shoes or rain gear. Another pound or two on the bike doesn't make a big difference, but panniers that stick out to the side seem to add wind resistance at high speeds (I've tried it back and forth). A bag on top of the rack seems to have no negative effect. I imagine a handlebar bag would have even worse wind resistance issues, and sometimes I'm biking 40 miles with stuff (again, shoes and rain gear). I wasn't able to find a hangs-off-the-rear-of-the-seat bag that was big enough to carry shoes, and if I could I imagine it would be big enough to have that wind resistance issue.

Also, a lot of us (me in college, for sure) don't have room to store multiple bikes. Personally, at the moment, I own 2 bikes (well 3, but that's just because I haven't bothered getting rid of the 3rd one yet - it might make a handy don't-care-if-it-gets-stolen bike). I could easily see owning 3 though - you can't combine a road bike and a mountain bike and end up with a bike that's very good at doing either. There's 2 bikes, and my 3rd is a winter bike - here in Minnesota you'll run through an entire drivetrain every year if you bike commute in the winter on your mountain bike, not to mention frozen cables and deraillers, so I bought a dedicated winter bike with an internal hub, enclosed cable housing, etc etc that also doubles as a grocery store / coffee shop "not to fancy to leave locked up" bike in the summer. But I certainly wouldn't let a little thing like not putting a rack on my carbon bike force me into buying a whole 'nother bike.