More or less the same, yes.
Something I started doing last year is to make a list of the eight or ten comparable books published in the same category on Amazon a day or two to either side of my new releases, and to go back and see how they're doing, periodically. (Comparable books in the sense of standalone versus standalone, say, and sub-$3 ebook-only versus sub-$3 ebook-only, et cetera.) It helps put things in perspective, of sorts, when you look at someone who's published, say, seven books, and not sold a single one (on Amazon, anyway...) four months later. Quantity, it seems, isn't always an instant ticket to sales.
But it's dangerous, IMO, to try to study those folks and their books too hard, to see what they did wrong. There's no book out there the groupthink can't come up with a dozen major "problems", real or imagined, with, after all, and it's really hard to deny the role luck plays in self-publishing. Are all those unsold and forgotten books badly written? Are the covers misleading? Amateur? Are the blurbs unattractive? Are the titles off-putting? Are the books, against all odds, just too damned niche? Are they listed in the wrong categories? Were they released too soon together? Too far apart? Or... were the writers just unlucky? If they'd stuck it out for another half-dozen books, might things have been different? The Shadow knows, but the rest of us can only guess.
There's also the whole question of how you tell when someone's had a final meltdown and quit for good, I suppose. Remember Franklin Eddy? He put out three books in June under that name, one in July, and... one in October. Has he quit? Has he died? Has he switched to a less-tainted pen name? I dunno. Jackson Jones used to post here on KB all the time, but just quietly disappeared in late July, and his books are no longer on Amazon, or anywhere else. That one crazy ultra-racist guy left KB, thankfully - but he's still writing. A lot of the "warriors" that thought e-books were The Next Big Thing have gone away (thankfully) to chase the next pipe dream, but not all of them, and it's hard to say how many might come back the next time some idiot guru tells them about some nifty new way to game the system in just two hours a week, or whatever...