A company would have to become an ICANN registrar to be able to register their own domains, in addition to having to setup registration agreements in every other country TLD that those companies do business in (google.co.uk, microsoft.ru, etc.). That would require a lot more money and overhead than just letting MarkMonitor do it, which specializes in this sort of thing.
I work at a consumer registrar, the only thing you need to do in order for us to hand over control of a domain to you is put a company logo on a word document, stamp it and fax it to us.
This does not apply to larger clients, but then if you're already looking for that kind of service it makes sense to go to a company that specialises in that.
I bet social engineering mark monitor is a lot harder than doing the same to even network solutions.
Now wikipedia is likely fine since EVERYONE knows it is important. But what about IBM's marketing campaign #249's 'desielenginesandyou.com'? If you were IBM would to trust registrar x's underpaid customer support?
