eBay redirects old product links to prop up arbitrary categories

I stumbled upon this by chance but was rather impressed to learn that eBay (with all their millions of valid IBLs) still finds it necessary to properly (301) redirect IBLs that point to old (removed after 90 days) auction pages and use them to prop up what seems like either a VERY loose match to the theme of the original auction or a completely arbitrary category listing.

I don't know if they've always done that but it appears to me that it's a somewhat new development because I remember going to old listings before I usually ended up on some sort of a custom error page (don't remember what HTTP code was returned but would not be surprised if it was 200).

So, if you guys have pages that expire, do you just let them die (404, 410) or do you reuse the URLs for different products or redirect the URLs in the way eBay does to save IBLs?

I guess, my major concern would be that the latest eBay approach seems to be creating a possibly unlimited amount of URLs on one site. It may be safe for eBay-size site, but would it be OK to do it on a 100,000-some pages site


P.S. This is OT but has to do with eBay URLs, too: last few months their redirects seem to be wacky in general. For example, NONE of the URLs I receive in any email communication from eBay appear to be valid. What gives?