I was having a conversation this evening with a fellow coupester who was convinced all Coupés have a switch in the glovebox that allows you to disable the passenger airbag with the key. His S reg LE has this feature, but rather oddly, my R reg 20VT doesn't!

I've been trying my best to convince my Mrs that the coupe will be a perfect family car (we have a baby on the way), but this latest revelation is slightly disappointing.

What's the deal? Is my coupe unusual for not having the airbag switch in the glovebox?

It was added mid '98 or so.

It may mean that your car was built before the LE in question, just registered after. I also have an LE with this switch in the glove box.
It's unlikley you'd be putting you baby in the front anyway isn't it
Back seat is surely a safer position. I had both my kids in the Coupe until I got fed up with moving the seat forward and them kicking me in the back
That was when they were in a stage 2 seat and 4 & 7 years respectively. I now use a booster seat in the front if required and leave the air bag on.
I had no worries, or accidents (touch wood)