If I was to go back to E3 2013 and add up all the games that Sony has announced with themselves as the publisher and add up all the games they've released thus far, they easily have more games announced than published.
Completely incorrect. They've shown 56 Sony-published PS4 games at their various conferences since 2013; 40 of them have released (71.4%), and 16 are still in development (28.6%). By comparison, Microsoft have shown 34 published Xbox One games; 25 of them have released (73.5%), 4 have been canceled (11.8%), and 5 are still in development (14.7%). The total numbers for both platforms are higher--see below--because not every such game gets shown onstage.
That's not even accurate. No way in hell Sony has published almost 300 games in 3.5 years.
I was listing all games shown at conferences, not first-party published games. But according to Wikipedia, Sony has published 77 games for PS4 (including those not out yet). Microsoft has published 43 for Xbox One (also including those not out yet).
I totally see your point about the possibility of development hell for long-timeline announcements. And I've often heard people say, like you do, "I have plenty of games to play, just wait on announcements until they're ready." But I think this misses an important factor: you've already bought into the ecosystem.
The games announced well in advance of intended release are meant to maintain continued excitement in the installed base, yes. But I think they're even more important to sway people who haven't bought in yet. There are few enough of those on GAF, so it's not a common outlook around here. Yet imagine if you didn't own a console yet, but were in the market. Would you rather hear just about games coming in the next 6 months, or would you like to also know what might be releasing in the following years?
This is why I think most games announced intentionally far from release are the "event" tentpole titles.* Those are the ones which more casual gamers--people who don't have a new console years into the generation, and only buy a couple of games a year--will find notable. I believe this "staking out general territory well in advance" is a factor in Sony not just having an installed base advantage, but still maintaining a 2:1 new-user buy-in rate over Microsoft.
* As my analysis found, most of the very longest dev times actually belong to smaller-scale games ("indies"). But I suspect these are likely unintentional and due to intrinsic and extrinsic challenges, rather than a specific marketing scheme.