yeah same here.... I have loads now, I don't see why they just haven't made it completely public but then again it still does have the erie of being cool without everyone being able to register.
Though saying that for a while now you have been able to register using a mobile:
https://www.google.com/accounts/SmsMailSignup1 but then it might only work in the USA / Canada like most of these things do... but if you use googlemail.co.uk then you probably avoid this...