Sorry to be thick-headed, but why? It can still be dispelled just like Permanency, so I'm apparently missing something.
Dandu answered in a very succinct manner, but I like being verbose.
Basically, if you take Permanancy as a spell known, as a Sorcerer, you've got a problem: There's a sharply limited number of spells it applies to, and you're not going to use it often at all, because there's a very sharply limited list of things it can do, and those don't come up often. As a Sorcerer, things you're not going to use often, if at all, are a really bad idea.
Limited Wish, however, is useful in any circumstance where you can afford it - it's close to the ultimate "I need to be able to do X" spell. Direct damage? Check. Buffing allies? Check. Obscure utility spell? Check. 300 xp/pop. It goes well on any Sorcerer's list because there's a LOT of things it can do (including raising the dead, by way of Reincarnate - or Raise Dead, if you've got the diamonds).
So, as a Sorcerer, you don't bother with Permanency as a Spell Known - you do, however, bother with Limited Wish, as that's rather useful. You still won't use it every day... but it's an expensive swiss army knife all on it's own.
You know, I hear that here and elsewhere but I've yet to see it. I guess I've been just lucky but I haven't seen it anywhere else either. I'm currently running a Ultimate Magus who did the Permanency routine as a role-playing gimmick (he never expected to have to adventure!) and I was so afraid of that happening I actually wasted a ring slot to take a ring of counterspells. As a DM, I used to do it, but I got tired of all the dang checks.
It's table and DM dependent.
If the players use Dispels a lot to get rid of BBEG buffs, then the DM is more likely to use Dispels as well (as it's a reasonable tactic, and makes sense). If the players use lots of layered buffs, then the DM is more likely to use Dispels (as it becomes a particularly effective tactic).
If the players don't use lots of layered buffs, and (almost) never cast Dispel Magic, then it's rather unlikely the DM will bother using Dispel Magic either. So it'll show up in some campaigns, but not others, and will depend more on the group and the DM than it will on the rules themselves.
