I don't know if the developers knew this or not, but frag launched via HE is actually much better at penetrating armor than relatively low velocity projectiles from guns.

The frag loses its effectiveness as range from the detonation increases, but a 40mm round landing a meter from someone in body armor is a guaranteed kill "IRL".

I'd expect a direct hit on a Deathclaw to be a kill 99% of the time (a heavily wounded and disabled creature in the other 1% of times), and so should you.

http://www.newvegasnexus.com/downloads/file.php?id=36208... (and mine is not the only re-balancing mod out there)

They severely nerfed the Fat Man in FO:NV compared to FO:3.