"Group buying"? I don't think I'd call a bunch of individual customers a "group" just because they visited the same site on the same day. I also don't think I'd call the site a "group" because the site didn't buy anything, they just arranged a deal for the individual customers.
"Group buying" would be people coming together as a "group" and buying a LOT of 1 thing, then splitting it up.
If we're going to call Groupon "Group buying", every newspaper in the US (and possibly the world) has been doing it for decades.
Whether the term is semantically correct or not, "group buying" is how most people have been referring to those types of sites (either that, or "daily deal site" -- though even that, one could argue, is incorrect, since many of these sites have deals that last more than one day or present more or less than one day or present multiple deals in a day).
Your point is valid, I suppose, but the accepted nomenclature is the accepted nomenclature.
It is unfortunately accepted nomenclature, but still off and there exist models that are truly "group buying". This model is quite popular in China. Hundreds of people will show up in front of a big store in China in the morning and demand a 10% across the broad discount or else none of them will go in the store. That's group buying.
"Group buying" would be people coming together as a "group" and buying a LOT of 1 thing, then splitting it up.
If we're going to call Groupon "Group buying", every newspaper in the US (and possibly the world) has been doing it for decades.