I wasn’t too surprised about getting downvoted. I suspected that some might find “the solution is simple” a bit brazen, but I wasn’t sure how old the thread was, and wanted to draw some attention and critique before the thread died. My next line was more honest “I suspect that the reason…”. :-)
As for why a curling stone is different than a beer bottle or upturned glass on a table, that wasn’t the goal of my thinking. I was only trying to explain the curling stone. In any case, while having some similarities, the two scenarios are still pretty different. As laxd points out below, the beer bottle and glass have higher centers of gravity which make the “leaning forward” line of thinking seem more reasonable.
As for the effect of pebbled ice, it seems reasonable that the difference between the static friction coefficient and kinetic friction coefficient is greater for pebbled ice than for smooth ice. And if static friction and kinetic friction are approximately the same for smooth ice, then this effect would not contribute substantially to curling on smooth ice.
This was a fun problem to think about. I had hoped that a smarter physicist would tell me why my hypothesis was bogus. As a friction expert, Nyberg almost certainly entertained this idea at some point. I may send him a message to see what it is that I’m missing.