Okay, I'm less grumpy and have some actual input after a lot of digging.
First, I don't see anything specifically saying that mecha can't get any magical enhancements. I was under the impression that something like Greater Magic Weapon was acceptable. Mecha aren't really gear though so it makes sense. I don't think that the restriction on permanent magic enchantments should change, they already get attack bonuses and special effects, and also the ability to have a lot of different weapons and attack with a handful of them. Regardless, removing Force probably makes sense in a non-mecha game.
After looking at the Real and Super robots, I think this might just be a Maid issue. Robots get all kinds of other stuff (and super robot built-in weapons can just easily get bonuses anyway) and you can choose to not be in your mecha, whereas Modern Maid (at least to me) feels like it is meant to replace normal gear with Arsenal weapons.
I see two basic easy options, either or both could be used (on top of removing Force). First, you could add something like the following to "Mecha Material in Non-Mecha Games": Mecha weapons are treated as wielded weapons for the purposes of temporary magical effects that enhance weapons. Second, you could add to Modern Maid that arsenal weapons can bypass damage reduction as if they were magic. It would go either in either the second Elegant Maid choice (making earliest level 4) or in Perfect and Elegant Servant (making earliest level 8).
Since the Gauntlets (the cheapest magic item with an overlapping effect) can't be purchased until level 6 with the "can't spend more than 1/2 WBL" restriction, tacking the ability on at level 8 would make sense.
If you're concerned about this letting gestalt SRW classes get free DR bypassing, you could restrict it to just Maid arsenal weapons. If you do that, it would be a good idea to put something in the Chobit ACF about how their racial arsenal weapon could as a Maid arsenal weapon for all purposes (except quick replacement without needing a level up if you want to keep that restriction).