I think it's a case of supply & demand. So long as blockbusters like Wicked keep getting box office receipts of 100%/week, then the prices will keep on rising until the demand slows down (at this point in time, seemingly never...). When the anticipated public appetite for a show isn't that big - that's the only time when tickets seem discounted. Example: the new production of Rent in London, General Admission for £30 ($60 - a far cry from $125 for Hairspray at the Shaftesbury), but the show isn't going to last for much longer beyond press night despite the competitive pricing policy. In this scourge of a capitalist society, something's only worth what the masses are willing to pay for it - obviously there must be idiots willing to pay upwards of $450 for YF and (most importantly) enough of them, IMO that price doesn't get plucked out of nowhere. It's just a massive shame for many of the people poised best to actually appreciate musical theatre (i.e. BWWers, although I don't mean to make general assumptions about your respective incomes), these prices often seem absurd.
Why, hello Margaret! Yes darling, half past five. Well, everyone, simply le tout Park Avenue and la creme de Hyannis! Well, the press table's going to be awfully crowded... but if you don't mind sharing a folding chair with Harper's Bazaar... Sing? Me? Heavens no, it's Edie's day, not mine... Although people can be so insistent, and I hate to disappoint. Twist my arm, blackmail me, threaten my very life, and who knows? You might get a verse of something...