And there are users of Firefox out there with >15000 tabs.
Two reasons for tab hoarding: 1) spatial -- related tabs are close together (frequently open a bunch of related search results; if I come back to them to continue later, they're all together). 2) history -- unlike bookmarks or history entries, tabs retain the forward and back history, so when you return to them you can know how you go there (go back to the search for example).
I do periodically clear out tabs, especially duplicates. The Tab Stats extension by glandium is very handy for tab hoarders