Took a quick look at your 1000 list and it seemed swarmed with those oneline posters! I have also noticed some of these users but I couldn't understand what they were up to! I got the spamming part but apart from that, what are they really trying to gaining by making these oneline posts? Will anyone enlightened me! 
So a person can make infinite amount of accounts with an invalid mail using the same IP with ?
As long as it hasn't been blacklisted? Or is there any limitations? Like 10 account per IP or 1 account per day per IP?
They can easily use invalid email instead. Bitcointalk gives people privilege to register without a valid email. Such a person will just input what comes to his mind as email and he will likely get registered and start posting.
So a person can make infinite amount of accounts with an invalid mail using the same IP with ?
As long as it hasn't been blacklisted? Or is there any limitations? Like 10 account per IP or 1 account per day per IP? yes but remember that there are reasons, for privacy and security
Let's remember that the outside world is just waiting to understand that you are doxing yourself and harming yourself in some way, so these security measures are useful.
if they are abused, just punish those who abuse them
There should be a sort of "note" like on altcointalks that then disappears when these cases occur