Now, I know the rationale for this. They don't want an army of friendwhores befriending every damn person out there in order to draw a kneejerk friending reaction. It gets really messy and arguably damaging to both LJ's social and hardware infrastructure when people do that crap.
But still, LJ is also an RSS/atom newsreader. It's quite possible to make RSS filters for specific subjects you are interested in (weather, local happenings, local news, politics, gaming, any subject you can think of), have several (or several dozen) feeds, communities, or "friends" relative to the subject, and if that's the way you work, you can rack up several hundred friends that way, easily.
In my case, I have been on LJ for over six years now, and have about twenty custom friends groups for all sorts of subjects, interests, and people I like, plus special ones I've created for subjects like military journals/weblogs, katrina survivors, technology, art, etc. Each category represents a lot of research that I've done, and all of them feed me a constant flow of information that I find useful and informative. I've long since passed the ability to read and respond to all of my friends everyday, but I still check in pretty regularly to find out what people are up to, even if I don't always have a chance to reply, and that's good enough under the circumstances.
Now, I admit that my circumstances are, by LJ standards, quite unusual... but it will likely get to be more common that people use their LJs a bit more like me as they go along. Unfortunately for me, after six years, I've hit a wall. That means that unless I do either some ugly kludges or some ugly prunings, it will also be harder for me to follow and write about the next big thing, whatever that happens to be. Could be a massive earthquake, another war, a student uprising in China, or anything, really... but by hobbling LJ, LiveJournal also risks hobbling the quality of the content available on their site.
If you keep using LJ, you may find yourself hitting the same wall someday. It might take you a decade or so, and you might be shaking your head now about the absurdity of having 750 online friends, communities, RSS feeds, etc. that you follow, but keep in mind, you used to think that you'd never need more than a ten gig drive, too. Maybe you will travel a lot, or develop a larger audience someday, in which case you really could find yourself with hundreds of online friends. It certainly isn't something that LJ should arbitrarily discourage, is it?!
It seems to me that there shouldn't be a limit on how many friends you can add, but rather, on how many non-syndicated friends and communities you can add over a given period of time, and that free accounts could (and probably should) be capped at a lower number than paid/permanent/early adopter accounts.
Why not, for instance, limit free accounts to something like 250 friends + 50 per year (possibly with a cap on the number of syndicated feeds they can add -- 50 or so, perhaps) ... or paid/permanent/early adopter accounts to approximately 500 friends + 100 per year (with no syndicated feed cap). Or simply remove the cap entirely for paid users with a couple years under their belt -- they could be assumed by then to be trusted users who aren't likely to abuse the system.
It simply doesn't make sense to treat powerusers like potential abusers. 'Nuff said.