Google has not yet reached a decade in its existence. In fact it’s just celebrating its 9th year in business. But look where it’s at now. Pretty amazing. Happy Birthday Google!
..you don’t even need to submit your site to Google.
But why does the Google submission page still exists and continues to fuel the age-old belief that we really need to submit our sites to Google (which contradicts the Webmaster Help message above)?
There is an ongoing discussion about this if you’d like to know what the experts have to say.
Personally I think it’s not something that really warrants too much attention. The Webmaster quote exists to support the idea that it is not necessary to use the URL submit form. At the same time, it won’t hurt your site if you tried submitting it using the form. Or submit a sitemap using its generator.
Similarly I can think of it as similar case (not exactly the same) as Gmail service. Before, one can get a Gmail account only when s/he is invited by a Google Account holder using the form found within the Gmail interface (after logging in).
When Gmail decided to open up its doors to everyone by providing a sign up form at its homepage, the Gmail invite remains in place within its interface.