Hussar
Legend
So Hussar, you would feel better if we pointed out that a fighter trying to negotiate with a demon for a wish was going to have the same difficulties as a wizard? Consider it pointed out. The point is that the fighter has the option to arrange it, same as the wizard, albeit through different channels; not that the fighter will have an easier time of it.
Firstly, your reading of simulacrum is rather generous. Generally when you do a polymorph or the like, spell like abilities are not granted. The spell text, as I read it mentions nothing about duplicating spell like abilities so I wouldn't allow it. In point of fact, the spell specifically limits powers to Special Abilities appropriate for the HD, which for the Glabrezu would be rend. The creature is an illusion, not the real thing. A DM would be well within the rules to never give a simulacrum the ability to grant wishes (or cast any other spells for that matter; at least without using other spells in the creation, or via DM approval). Besides which, even without the spell text, I know that a 7th level spell should never be used to create a 9th level spell effect ex nihilio, so your understanding of the spell is somewhere flawed.
Well, from the text of the spell:
It appears to be the same as the original, but it has only one-half of the real creature’s levels or Hit Dice (and the appropriate hit points, feats, skill ranks, and special abilities for a creature of that level or HD).
Since this isn't a polymorph and it does specifically say that it gets the special abilities, you've pretty much reworded the spell.
Secondly, I would rule that a lesser planar binding was a type of summoning, which means that the demon and all its gear disappear from the mortal plane once slain. As well, in many cosmologies, when a demon is "slain" on the mortal plane, its not really dead; just barred from returning to the mortal plane for a period of time.
Again, from the text,
Conjuration (Calling) [see text]
Additionally, if you actually went to the PHB, they specifically state that anything called this way and slain, does not just get barred. It's actually dead. This is why Planar Binding won't allow you to make suicide troops.
Thirdly, such bad faith summoning is not going to make demon lords happy with you.
Yes, because demon lords keep perfect track of the infinite number of demons in the abyss. The Chaotic lords of evil have perfect record keeping that would let them know that I've done this. Sure.
Now, let me hasten to point out that a fighter which pays for a demon to be summoned in the same way is going to have identical problems.
If by problems you mean DM's who will ignore spell text, rework mechanics and then use the setting to beat them about the head and shoulders, then I agree with you.