When The Producers opened on Broadway in 2001, its immediate success led to the introduction of so-called “premium” seats – where the producers, in effect, turned into their own touts, selling off the best seats in the house at inflated prices (on that occasion, $480 a seat), which has now become adopted as an industry standard practice in New York, though never with prices at that fleecing level. For Mel Brooks’ new Broadway-bound show, Young Frankenstein, the premium seats have already been pegged at $450, before the reviews are even out and therefore the likely demand for them is not yet known yet.
Now Young Frankenstein’s co-producer, Robert Sillerman, has told the New York Times that they are going to break ranks, too, with the Broadway custom of reporting their weekly grosses – a practice, dating back to the 1930s apparently, in which the weekly figures are published in the pages of Variety (and now online, too, in places like Playbill.com). According to Sillerman, “This is a private transaction. Consequently, I don’t know if there’s any – I’m quite sure there’s not any – bona fide business reason to do it other than bragging rights.”
No other private industry feels compelled to disclose its weekly balance sheets to its rivals, so why have Broadway producers traditionally honoured this practice? To borrow a song title from that great Broadway musical Fiddler on the Roof, the answer may simply be “tradition”. And there’s also a suspicion that a producer who doesn’t want to give the game away may have something to hide: that his show isn’t doing as well on the advance front than was expected.
But where one leads, others may follow; and the days of full disclosure that Broadway currently operates under may well be numbered. As Mr Sillerman told the New York Times, “Every producer I’ve queries about this had said, ‘Hosannas to you’. Every one of them has unilaterally applauded the idea.”

I think when you hint that the advance is something that,at this point, may be dissapointing - you've hit the nail on the head.
The show didn't sell out it tryout in Seattle , depsite mostly favorable reviews.( and yes it was a huge theatre but they booked a huge theatre thinking they would sellout- much like the too big for comedy theatre they've booked in New York) .
If the advance were huge there would be press releases galore about it, which would create heat around the show , which in turn would create a demand for tickets, which could then lead to them putting more seats on sale at the ridiculous $450 price. By not disclosing the grosses there will be no general knowledge of how the show is doing and so the consumer will be relying onthe honesty of NYC box office people and ticket brokers to purchase their tickets and my guess is that those people will be telling them that the "only" seats available will be the $450 ones.
As for Mr Sillerman's praise from his fellow producers I'd take it with a grain of salt. I can't recall a show that is coming into Broadway with more schadenfruade wished upon it.
"I think when you hint that the advance is something that,at this point, may be dissapointing - you’ve hit the nail on the head. "
This is part of a description on Theatre Board allthatchat of the line at the box office to buy tickets yesterday:
"The line to buy tickets extended all the way down to the New 42nd Street studios, half way down the block, and was moving slowly so I shudder to think what it's like now with the lunchtime crowd there. There were journos interviewing people on the ticket line. It's been a long while since I've seen a line like that on Broadway"
There was an additional line to sign up to a special lottery for 8 sets of tickets to each of the first two weeks of performances that caused a separate riot of interest yesterday too.
I suspect it is more shame at the ridiculously large weekly take that will keep the figures secret, after all it may well have caused a back lash against the show when the millions started showing up each week. Also remember that they are keeping it flexible about what is charged for many of the seats, there is no published list of exactly what row and seat cost what for each performance, they are squeezing as much out as they can and the tickets that don't sell will probably be sold at usual top rate nearer the shows date.
Whatever the truth of Young Frankenstein's sales, I find it eminently plausible that Robert Sillerman has been praised by other producers. After all, who in their right minds, if they thought they might EVER have something to hide, is going to be in favour of constant disclosure? And as Lee has pointed out above, that "something" might on occasion be excess rather than paucity.