I get about 4-5k miles out of a set of tires on my bike. Michelin Pilot Powers, I have over 12k miles on the bike and I'm on my 3rd set of tires. At $350+ a pop installed that's not cheap.
I'm not arguing tires aren't going to be a serious expense, but I think you guys are overstating the case. First of all the bikes most of us have are not good in terms of efficiency. Touring tires for a touring bike ought to last longer and and be less expensive. Assuming more of a beater bike / work horse instead of a performance toy, you can also get free tires with holes and patch them yourself. I know some older guys that do this quite a bit. Second of all, who sold you those tires? I got the same tires for $158 shipped and $70 to install on my gsxr. $230 ain't exactly cheap either, but it beats "$350+" handily.
In comparison, I have 90,000 miles on my car and it is on its 3rd set of tires. If I rode the bike 90k miles I'd have spent over $6000 in tires alone. Also, the bike is coming up on its first valve check at 14,000 miles and that is NOT an easy job. It will cost me a few hundred to have that service performed.
Yeah, valve checks will probably be the biggest problem. I'm guessing the change interval is longer for touring bikes though.
Also, shouldn't you factor in the price to purchase your bike vs the car?