i don't know where you're going with this post.
there's plenty of posts here about the longevity of these motors. mine is still going strong and it's a litle over a year old, with a lot of miles on it, and goes a lot faster than 28mph. i still trust it to make full throttle runs all day, everyday ('cept now, 'cause it's raining.) i average 10-30miles a day, and on a nice weekend have no problems blasting around till the tank's empty, putting in anywhere from 70 to 150 miles over the weekend.
i also never wait around for my bike to warm up, and once i'm on it, i'm WOT all the way.
i dunno if you're saying ebay kits are different from others, but they're not. everyone gets them from the same suppliers, and there's only a handful of different brands out there. it's not like they have an "ebay only" discount junk pile.
when you say "...without any aftermarket fixerupper parts..." again, i dunno what you're trying to say. if you're talking about the levers, plugwires, chains, etc, then i agree. those parts are pretty lousy, but if you mean the actual engine and it's related parts (carb, exhaust, CDI, etc) usually you can run the stock kit parts for a long, long time.
sure you're gonna have to work on it from time to time, but most of the problems have already been identified. everyone knows their exhaust cap is gonna come loose, that their chain is gonna "stretch," and that their gas tank studs are gonna leak... it's always a work in progress, but if you know what you're doing, none of these things will cause you any real downtime.
the reason they're only capable of 28 (+/-)mph out of the box is mostly due to gearing, and i think that's a pretty wise choice, since the average builder isn't using a bicycle designed for higher speeds anyway. but with a small amount of work, these engines can easily exceed 40mph. my bike has the stock carb (modified) and the stock exhaust (modified) and is capable of speeds, well, i hate to post numbers without proof, but lets just say if i squeezed a few more mph out of it, i could ride in the slow lane on the freeway.
so whatever you're trying to say with that picture, i'll cross that bridge when i come to it...