Perhaps AM meant for the third link to read: Re: How do I add commas to a number?

As to your second question, this seconds AM's first two reading recommendations. You're looking to learn the difference between "lazy quantifiers" and "possessive quantifiers." If it's easier for you, try reading "Mastering Regular Expressions, Friedl (O'Reilly)" or the "Regular Expressions Pocket Reference, Stubblebine (O'Reilly)"