Well it would have to make sense too I guess. I mean, not everyone has the resources/blueprints/science skill to create new EW's.
But there's a crap load of stuff that can be done really since we have pulse, laser, plasma, fire, other? (I wanna say acid, lightning and black materia (black hole thing, like that rifle in Red Faction Guerilla that dissolves buildings and people.))
If you go by that reasoning, normal guns leave even less room for different types, after all, you just have guns that shoot bullets. They can shoot bullets of different types, they can shoot faster, and be more accurate, and such, but they're still shooting bullets. If the designers aren't going to do energy weapons outside of your standard plasma, laser, and such, they could always just, oh, maybe add DIFFERENT KINDS of laser weapons and plasma weapons in the game. Because you know, it's possible for more than one model of laser-based or plasma based rifle or pistol type weapon to exist in the same universe... After all, in Fallout 3, we had two assault rifles, not counting unique ones, which functioned pretty much the same way but had different stacks, and for pistols, we got many more options. There's no reason we couldn't have more than one type of laser rifle or laser pistol too, or for a bit more variety, how about a laser sniper rifle? I'd imagine lasers would be good for that, considering that you wouldn't have to worry about things like the wind or bullet drop messing up your aim at long ranges. Or maybe some sort of automatic plasma weapon or something, not only would things like that add more variety to energy weapons, it could also allow them to cover certain niches that they did not in Fallout 3 (Well, Operation Anchorage added the Gauss rifle to serve as an energy sniper rifle, but it made absolutely no sense for it to be an energy weapon since it doesn't shoot lasers or plasma or anything like that, it shoots a solid projectile, you know, kind of like what the 10mm pistol or assault rifles shoot, only the bullet is propelled by electromagnetic coils rather than exploding gun powder, but if that allows it to qualify as an energy weapon, then really, ANY gun should count as an energy weapon.)
But we do know that there will be more types of energy weapons than in Fallout 3, at least a couple ones that weren't in Fallout 3 have been confirmed, still, I expect that players who focus on energy weapons will have less options than players using guns, so I hope that energy weapons will get some advantage to make up for this, like say, being more powerful than their normal counterparts, not to the point of being unbalancing, but enough that you would actually have a reason to consider sacrificing options for the sake of energy weapons, it makes sense to give them some advantage anyway, after all, people wouldn't bother making energy weapons if they didn't have some sort of benefit. I don't think "because it's cool" is reason enough for the military or any other such group to invest in such weapons.