Does it affect site ranks on search engines?
No, unless your target keywords are digits like 2, 8 or 100. But who use that keywords anyway?
Do you think people will be less likely to visit it?
Short answer is no, unless the URL is packed with random digits. That being said, depending on what kind languages your web site is for, some languages have very intriguing properties. In Chinese, 8 is a very good number, equals prosperity, and 51 means I want, that is why in artlung's list there are 58.com, 51job.com. In Chinese, those are very good name. BTW 630 means something even in other langues, does not it?
Is this just a programmer response, since most variable names can't start with a digit?
Negative, as far as I know.