Just anecdotal evidence here (my own, for what it's worth) - back between 1985 and 1989 I had amassed a collection of somewhere around 2500 diskettes worth of Apple ][ software which I collected mainly through mail trading with around a half dozen people I contacted (or contacted me) through Computist magazine and some things from the BBS scene, usually newer releases. I had them all cataloged and categorized in an AppleWorks database. I remember going to a couple of Warez trading parties in Austin, TX around 1989 where I and my best college bud brought all of what we had in 2 suitcases - kind of like the mob showing up, is how one of the attendees described it at the time. With that being said, it was nearly impossible to find something we didn't already have that wasn't some variation on things already in our collections. Sure we could have added 100+ EAMON adventures but we were more interested in the commercial stuff, so more often than not we passed on stuff like that. So I'd have to say that even in 1985, the claim of 10,000 software titles was being at least somewhat deceptive. If you're counting every single program on, for example, the DOS 3.3, PRODOS and Beagle Bros. utilities diskettes as a software title, then I'm pretty sure that number is accurate. But as for that many actual commercial products you could purchase individually, I'd say that's quite an inflated number.
As for what happened to my collection... sadly, UPS lost EVERYTHING when I shipped it all home to PA at the end of my Spring semester in 1989. But it ended up being bittersweet, as I replaced it with an Amiga 500 (a decision I've never regretted) with the insurance check I received from UPS and used that up until 1998 before finally moving to a Win98 PC.
Anyway, yes, it is definitely cool that someone is finally creating a database of Apple ][ software. It's the platform I used during some of the happiest days of my teenage years and brings back many wonderful memories.