Because according to this book it does:
Page 64 - > Quantifiers and scope - paragraph 4.
I personally think that the former translates into, 'there exists an x, such that if Ax, then Bx', and the latter saying 'if an x is Ax then Bx'.
In this specific example, the symbolization key is:
UD: people Gx: x can play guitar Rx: x is a rock star l: Lenny
So here, it's:
∃x(Gx -> Gl) ∀xGx -> Gl
So for me the former is stating 'There exists someone such that if that someone plays guitar, then so can Lenny'. Where the latter is stating 'if everyone can play the guitar, then so can Lenny'.
So, the former seems to be picking out a specific member of a set, not just any member, but some particular person. The latter seems to be referring to every member of a set.