As you say, Polycarp, the question is sailing rather close to IMHO territory, but here goes:
1) Is there always at least some Champagne imbibed?
I’m pretty sure that I’ve seen celebrations where there were at most a couple of bottles on hand (which were sprayed), and no sign of drinking glasses anywhere. Champagne swigged from a bottle passed around would be messy and counterproductive, so there should be glasses available if any appreciable consumption is expected. I’d be prepared to bet that at many Champagne-spraying ceremonies, total human consumption is zero.
Googling “Champagne for spraying” turns up a cached link for a London go-kart track that may be rented for corporate team-building events, and offers:
(bolding mine). Perhaps it would be illegal at this location to drink alcohol, but spraying it is OK? Or perhaps their “champagne for spraying” is non-alcoholic?
2) Do they use cheap Champagne for spraying?
As BwanaBob says, it’s often a fairly expensive label. Veuve Clicquot Brut Yellow Label runs about $34 for a regular bottle (750ml). Not “Dom Perignon expensive” (~$100 and up), but not Cook’s ($4) either, although the latter would be just as good for spraying.
It’s not easy to find on-line photos of the spraying “ceremony” with the label exposed, but here’s one. That’s a Piper Heidsieck Extra Dry ($25) that he’s holding.
Wikipedia seems to agree that they often use the fairly expensive stuff:
3) Who pays for it all?
As mitchythekid says, it’s a business expense anyway, but I suspect that in some cases it’s donated by the Champagne maker, perhaps with a requirement that the label be clearly exposed to the cameras. In this photo, the guy’s being doused by a magnum of Mumm Cordon Rouge ($67), but if you notice the “celebration” bottle has extra “Mumm” labels in large letters. These extra labels are both “right-side-up” and “inverted” with respect to the bottle. Now, unlike still wines dispensed behind some bars, Champagne is never served from a bottle that sits inverted, so there would be no reason for the label to be readable that way unless it’s a special “event” bottle provided by Mumm & Co for high visibility. Even if it’s full of real Cordon Rouge, it’s still not very expensive for a Champagne maker to donate and it’s potentially good advertising.
[And, on preview, I see that Dewey Finn has already proposed this.]
4) What about celebrations in Muslim countries?
Thanks for asking! Champagne-spraying has been banned from the Bahrain Grand Prix (Formula One Auto Racing).
[Prices quoted are from Beverages and More. They are well-priced and have an extensive selection on-line. I am not in any way affiliated with this company.]