Note the "lifetime" part says updates - not upgrades. Which usually means once the version number changes (i.e. from 3.xxx to 4.xxx) the "lifetime" deal is up.
Also, if past experience is any guide, best adopt a caveat emptor perspective when dealing with FL-anything licensing terms.
Don't know if the leopard changed it's spots recently, but FL has played some interesting games with "lifetime" offers in the past. In one case, they actually sold lifetime licenses (as an add-on extra). Later on, they basically just changed the name of tha app, insisted it was a totally "different" and completely "new" product - and then refused to apply the old "lifetime" license to it.
A lot of customers were ticked to discover they needed to pay again if they wanted the new version.