True, but most of these instances, a person has been specifically targeted. Therefore they must have been known in the first place. Now the plan is to record everyone's emails regardless if your are a suspect or not. Another example would be to say that the Police take the DNA of a suspect but now the government has decided to keep a database of everyone's DNA just in case. OK that might be a little more extreme but honestly at the rate things are going i wouldn't be surprised.
But the aim i was trying to get at is a technical one. Can ISPs tell the difference between web browsing and webmail or me using MobileMe? If not then surely people who want to do harm could communicate via these methods and not have their emails tracked?