If you look at the top 10/100/1000 addresses
I've never believed these "top N" addresses things to be worth anything especially for coins with known questionable mining that are going to face scrutiny for it.. The first thing a scammer would do in that situation to try to get away with the instamine (after claiming it to be an accident) is move the coins around to a bunch of addresses and claim they've been redistributed so the instamine doesn't matter any more. As long as addresses are free these lists mean nothing.
That's a fair point, but it doesn't change the fact the over 70% of namecoins sit in 100 addresses, while that number is about 55% for vertcoin, 53% for litecoin, and about less than 20% for bitcoin (the most widely distributed coin according to these metrics).
I still don't believe these lists or calculations of concentration by address (as opposed to owner) mean anything at all.
One big factor is how much of the coin is at exchanges (i.e. many owners, few addresses). Bitcoin has the best developed infrastructure for thin wallets, mobile wallets, hardware wallets, paper wallets, cold storage, etc. and is also somewhat less dominated by speculative activity (virtually 100% of activity for most alts) so it stands to reason that less of it would be held at exchanges.