No there is no such thing as lifetime membership offered at the official LW site. I think if you double-check your browser history you will find you did not go to the official site but a scam site. Unfortunately people google LimeWire & the first results shown are those belonging to scam sites because they pay to be listed first.
See sample here:
http://www.gnutellaforums.com/open-d...s-success.html