They were never under any obligation to use mtgox.com for their original idea for all eternity, and on HN of all places there is no shame in pivoting to a better idea.

There's no shame in a pivot, but there's also valid reason to criticize a pivot to something you can't handle. Trading cards is not like trading currencies.

The person who started the card-trading site is not the same person who currently owns MtGox. The original owner did convert it into a Bitcoin exchange, but then sold early on (I believe pre-2011 spike) to let someone else deal with the hassles.

I'm aware of that, but it's not relevant to the point I made. If the original site was re-purposed, it doesn't matter who currently owns it.