I don't really agree with that. Well at least not for stuff in the US. I would spend the extra couple bucks for a flat rate. But some people want it as cheap as they can. If they select first class its most likely a bubble mailer. Not that long ago many group buys used them. I haven't been involved in any for a long time so who knows now. My .02
As I already said, the cost of a bubble mailer vs. the cost of shipping in a box is negligible. You can buy boxes and bubble wrap or even re-use bubble wrap and you're spending all of $0.10-0.25 more per package than a bubble mailer. When I ran my GB, I upgraded everyone to boxes instead of the originally planned bubble mailers since the weight ended up being the same (or damn close) and the cost difference was marginal.
My point is that there is no excuse to ship caps in a bubble mailer, not when you're charging as much as he is for the caps and shipping. If you cannot properly package the caps in a way that would protect them and you do not purchase insurance, you should be held responsible to give a refund or replace them.
The only time I've seen bubble mailers sufficient for caps is when they're laid out flat, sandwiched between cardboard and taped like that, then placed in the bubble mailer.