1. Are you claiming there are millions of spammers sending 10 each? If so, your definition is different from Twitter's. If it's just a future worry I'm going to cross that bridge when we get to it.
2. I don't know if it's easier, but it's certainly not easy. Otherwise gmail and twitter wouldn't have spam anymore. It's easy for spammers to pretend to be somebody else. Get a new username, a new IP address, forge headers.
Even if it's only 10 spammers, Twitter can't see that. What they see are a million different spammers. So they already have to deal with the problem you claim is harder.
2. I don't know if it's easier, but it's certainly not easy. Otherwise gmail and twitter wouldn't have spam anymore. It's easy for spammers to pretend to be somebody else. Get a new username, a new IP address, forge headers.
Even if it's only 10 spammers, Twitter can't see that. What they see are a million different spammers. So they already have to deal with the problem you claim is harder.