Okay, so maybe I overshot on the insurance estimates. However, a couple posters above mentioned investing the other money, which alters things again.
So here's more math:
Let's say that the ZR7/Nighthawk/Bandit owner loses $3000 on the value of the bike for 10 years, the HD owner loses 0, and the HD owner only pays $1000 more over ten years (a somewhat generous underestimate) for insurance. Remember the HD owner spends, say, $2000 more on customization than the standard-bike owner does. However, remember that if all other factors are equal, the Japanese bike owner now has $12,000 of cash left over. Let's say this person is very conservative, and chooses a savings bank instead of the stock market. They earn only, say, 3% APR (investing in the stock market could make a much higher annual yield). However, after 10 years, that 3% APR means that they make over $4000 in interest on their cash.
That means that after 10 years, the Harley rider will have lost $4000 more than the Japanese standard rider.
Another factor is for people like myself, who don't have $18,000 in cash handy. Financing a bike is little better than high-seas piracy--in the end, you'll pay nearly twice the value of the bike if you sit down and add up all of your financing payments. Many people have the ability to buy a new $6000 motorcycle with cash, but would have to finance an $18,000 bike--and they'd lose out big-time even if the resale value held steady.
In closing, let me say that if you just plain prefer the sound, feel, and ride of a Harley-Davidson, GOOD. Buy one and never look back (except when changing lanes, of course). But if you aren't devoted to any one type of motorcycle and you're very concerned with money, you can get a new 65-75hp Japanese standard and it will be easier on you financially in the long run.
Starving Student