This still doesn't explain why he asked for ID/proof of address after the customer register an account with mtgox. Being trustworthy is being honest, not deceiving your customers into putting btc/usd into your company and then ask them if you want your funds, give me your ID/proof of address.
MtGox and TradeHill both started out pretty much arguing that financial services regulations didn't apply to them because Bitcoin's legal status hadn't been legally defined anywhere. Each of them has encountered issues since then because of adopting that stance and it's likely that they'll be required to become compliant with local laws in more jurisdictions as time passes. The period of time during which they were able to get away without complying with such laws was a bonus for them and their customers, but it was naive to believe it would continue long-term.
Should both companies have realised at the outset that they would eventually have issues with financial services regulations and AML laws? Absolutely - and I suspect that they did realise that eventually their compliance would be required but they just didn't know when. To the extent that they're requiring either account or identity verification in order to comply with the law, users have little legitimate cause for complaint - the risk of the exchange bank accounts containing user deposits being frozen indefinitely if they're non-compliant is very real and always has been.
It's also possible that MtGox has taken this measure in response to attempted fraudulent withdrawals. God knows there have been enough threads posted here about people's MtGox accounts being the subject of unauthorised withdrawals that it would be irresponsible of them to not have measures in place to address that particular issue. The bigger the exchanges become and the more they're turning over, the more they're going to have to implement systems which automatically take actions in respect of user accounts and then manually review those actions if necessary. It's unlikely that MtGox knows what's going on with any particular user account unless it's flagged in some way by their system.
