Standard exceptions to the rule in recent memory include: - products that depend on 3rd-party developer support. If the iPad 3 has a new form factor and new ha

Standard exceptions to the rule in recent memory include: - products that depend on 3rd-party developer support. If the iPad 3 has a new form factor and new hardware such that developers will want to rewrite their apps to take best advantage, Apple might show it at the developer conference and tell everybody "you've got 3 months to get your apps ready" - products that get accidentally leaked or need to be leaked early due to regulatory requirements such as filing for FCC approval. What Apple doesn't do is float trial balloons just to have something to show. Lot of companies will mock up some design that is approximately similar to the expected final product and show/announce that, then finish figuring out how to build it. Apple's ideal is to make a big splash by showing something unexpected that you can buy in the very very near future so people run out and buy it, garnering additional publicity based on the big lines and big numbers of customers. Which is great if you can pull it off, though it seems inevitable that one of these days they'll guess wrong. If and when they do blow it, it'll be at least a billion-dollar mistake to have built up so much inventory in advance of finding out whether people like the thing.