It is indeed a big loosely-related collection of communities, from which users choose a la carte their areas of participation.
The Reddit my wife sees when she logs in is very different from the one I see, which is very different from the one fans of meme participation (rage comics, etc) see.
http://www.reddit.com/r/programming/comments/juzl0/what_does...
Extremely disappointmented this wasn't a picture of a dump truck full of bees.
2. Because programming is still a pretty big subreddit, I believe it's part of the default set: unlogged users and users creating an account will get prog as part of their default subreddit subscriptions. This brings "unwarranted attention" to the subreddit until the uninterested user realizes he can unsubscribe from prog. Things are getting better there as other subreddits have taken over as the juggernauts and are being ruined instead (gaming has 660k members, pics, funny and reddit.com have 850k)
Another good subreddit is /r/todayilearned
It's not that they view /r/all, it's that they have not customized their front page, so they get the default set of subreddits, which I believe is simply the subreddits with the most members.
/r/movies is full of spoilers.
/r/philosophy is shallow.
If by "maturing" you mean "attracting the fat middle and the tail end of the IQ bell curve" then yea, you're right.
I'm finding fewer and fewer reasons to stay on Reddit. If I had exactly zero time to waste, I'd spend exactly zero time on Reddit.
Which is why there is /r/academicphilosophy.
Like usenet.
(These are some of the subs that I like, they might not be your thing, but they're examples of solid communities)
http://reddit.com/r/truereddit
http://reddit.com/r/longtext
http://reddit.com/r/depthhub
http://reddit.com/r/askscience
http://reddit.com/r/neuro
http://reddit.com/r/burningman
http://reddit.com/r/movies
http://reddit.com/r/linguistics
http://reddit.com/r/philosophy
And if you're looking for pictures, there are the "SFW \"Porn\"" subs:
http://www.reddit.com/r/earthporn+villageporn+cityporn+space...
Reddit certainly isn't dead. It's just maturing.