Why would a serious cyclist buy a bike on eBay, new or used, that they haven't ridden, no matter how great the deal?
Because they can buy something they can't get locally, or something rare.
That 60% number is just fabricated, there are a lot of businesses and repeat sellers that make up the bulk of eBay, as for the other alarmist concerns, that's what the feedback policy is for.
If you buy from a local guy from an ad in the paper-do you get to see his last 100 transactions and if everyone was satisfied? do you even get this from a LBS?
If one gets screwed on eBay, it's because they dealt with an unreputable seller, this is the buyer's fault.
I've purchased several items new on eBay over on-line shops because I don't get screwed on UPS shipping rates to Canada.