Yeah they definitely use a regular bottle cap, which is why I thought of it. And around the holidays non-drinkers ALWAYS buy martinellis. The labels I've found come off very easily as well.
Yeah, I noticed that about the sparkling wine bottles just this last week. Had a couple over new year's.
a friend of mine did some beer in a couple once I found out and he said they worked great. I'm considering doing a test with a couple of 2 liters of soda to see if they seal well.