What is wrong about it? Would you prefer to have 2 GB shared quota, or separate quota of 1 GB each? With shared quota you have more flexibility as to what service you prefer to use more.
In that case, aren't you arguing that quotas shouldn't be placed on email at all? It's not like they instantly block receipt of mail if you go over the quota, you have time to fix it, which is much better than many mail services.
Not really, a gigabyte goes a long way for email and if you get a warning with 200 MB left or something you have lots of time to act on it.
In contrast to a video recorded even by phones today a gigabyte is consumed in no time. Accidentally (without realizing how big it is or how much quota you have left) uploading a short clip is not something you put a lot of thought into.
It's not like they instantly block receipt of mail [...]
Well true, but it sucks having to rely on googles good will for that, you don't know the hard limits and they can change at any time without notice. It is still unacceptable UX.
I once was over the quota for over two months in a row, and still had no problems sending and receiving email. So I think Google does understand that email is critical service :)