Would it really matter, unless you were cooking in large quantities? I mean, an Imperial teaspoon is a US teaspoon, an Imperial cup is a US cup–I’ve never had to worry about whether the recipe calls for US or Imperial, simply because I’ve never made enough to worry about, for example, US gallons vs. Imperial gallons.
I guess technically there is a difference. I use the terms interchangeably.
It would seem that the differences are too small to worry about for everyday usage in the home. I’m sure not going to worry about the extra 0.091 (or whatever) in an Imperial ounce.
Interestingly (and getting back to my point of “does it really matter”) I have to ask: what if some of my kitchen measuring devices were made in the USA and calibrated in US measurements, and some in a non-US country but calibrated in Imperial measurements? Will that affect my home cooking or baking? Or are the differences too small to do so?
For that matter, is my 355 ml (12 oz.) can of beer any larger or smaller than my American friends’ 12 oz. (355 ml) can of beer?
I doubt the differences are enough to affect any home baking, but I still wonder about professional and industrial-level baking. That could be end up being a benefit though. Changing proportions is one of the fun parts of cooking. A little trickier with baked goods, but still fun to experiment.
If I still drank, I would definitely consider that a valid research project. 
Maybe that why beer tastes better over there.
That’s actually a very good question. At some point this summer, I’ll be catching up with an old friend of mine who is a commercial baker. He has made rolls and such by the hundreds of dozens at one time. If I can remember, I’ll ask him. And if he can supply an answer, I’ll post it.
Actually, you gave me an idea for getting an answer out of my baker friend–I’ll ask him to help with a little “research.”