Caps are okay for white wines. Not very long aged reds or meads, and there are a number of commerial red wines I really don't like to drink anymore because of the switch. They're okay for a while, but they need to breath, in my opinion. It's not an excuse for tradition; there are a number of wineries in Canada that use new synthetic foam corks for their reds because they're porous. I think there is a lot more going on here than simple oxidation if the industry is recognizing it. There are many odd, often undesirable volatile compounds in a young red wine or a mead, like fusels, possible diacetyl, terpenes, alcohol acetates, esters etc. These chemicals, without anywhere to go will either polymerize, react with something else or just stay there. I have a hard time believing that heavier volatile organic compounds will just degas with the CO2. These compounds contribute to the flavour in positive and negative ways, and it's only reasonable to think that if over time they are allowed to dissipate somewhat, it might allow the wine or mead to mellow more than if these compounds had nowhere to go.
All in all, I use corks for meads because I like to hang on to the stuff for a long time before drinking, and having drank a lot of different wine for quite a few years (I live in a major wine region) I tend to think there really is a difference, based on what I've tasted, seen and conversations I've had with people in the industry. Caps are okay, up to a point. But there is just too much funky, volatile crap in a young mead to keep it closed up, in my opinion.