My reason would be that lynx is really slow. If any external tool, I'd use wget -qO - to pull pages (or maybe curl if you have that; it's less common than wget).

That said, I can't think of any particular reason in favour of using an external utility. I'd just use LWP::Simple; and call get(), which is one extra line to pull in the module and otherwise (at least) as simple.

A reason against using backticks in general is security; in your case, if $fetch_this ever contains input from untrusted users.