Checked again and I was presented with the login form after all… I have a bookmark to my activity and when I click it after I’ve been logged out I often end up at the new user registration form, which is pretty frustrating.
IMHO, if a website’s home page doesn’t have a place where you can log in, and instead makes you click a link labeled “login” which then takes to a login page where you enter your id and password, that’s poor design. In this case, you might try bookmarking the login page instead of the home page.
If the browser detects that you have been logged in before, you should get the login screen instead of the sign up screen.
The reason the sign up screen is default is because it’s more likely to attract new members. Users that have already signed up is likely to know how to log in.