It is very difficult to make assumptions regarding the data extracted from the wallets. Most of the individuals may be having more than one wallet (I myself have dozens of BTC wallets). Also, some of these wallets may belong to gambling sites, exchanges.etc. I would say that the only reliable information regarding Bitcoin ownership comes from the leaked Mt Gox data. Mt Gox had made KYC mandatory, so we can assume that the data is having a high level of accuracy. BTW, an user of this forum (rpietila) posted some stats a few years back. You can check them here:

https://bitcointalk.org/index.php?topic=316297.0