That's not true, though. You would still have to either press tab (now enter), or click the second field to enter the password.
Type username/password = ~1s each
Single keypress = ~0.1s each
Page load = ~2s
Before: username + tab + password + enter = 1 + 0.1 + 1 + 0.1 + 2 = ~2.2s
After: username + enter + page load + password + enter = 1 + 0.1 + 2 + 1 + 0.1 + 2 = ~4.2s
Roughly doubling the amount of time it takes to enter your information is significant and annoying.