Unveiling things by having a velvet curtain or cloth on top (and then lifting it up!) has been done for decades, perhaps centuries. It's not unique to Apple or to 37signals, it's a common occurrence that they were expressing digitally.
I'm not arguing with any of that, however these two works share a lot more than just the act of "unveiling", in particular they both reveal a small but identifiable part of a logo.
In both cases there's no physical product to unveil (one is a retail store that is too big to be unveiled and the other is a service with no real physical manifestation) so the graphical representation of the product is abstracted away to a logo which is being unveiled. Only showing a small (but identifiable) part of the logo creates a sense of motion, it tells a story. It communicates that there's something new and exciting going to happen very soon in relation to this well known logo. In my opinion this is a creative idea that indeed builds upon the old tradition of unveiling things but it also goes way beyond it.
