No en_GB option

You can select it later during installation, though. As a British English speaker myself, this doesn't really bother me all that much; it's not as if the boot loader text would be significantly different, and I want to avoid loading up the boot loader screen with too many choices. It's just there to let you get at a language you can read and a keyboard mapping that matches your keyboard in order that you can read the boot menu choices and edit boot options by hand if you need to.

I'm not saying we'll never change this, but I don't think it's a very high priority. At present, the only language variants that you can select in the boot loader are pt vs. pt_BR and zh_CN vs. zh_TW; there are good reasons for both of these, as they are really quite different languages, and the Chinese ones actually use different scripts. These arguments don't apply to en_GB, so it would have to go along with fr_CA, de_AT, es_MX, and so on, which would really require a new UI.

In the duplicate I filed, my objection is that this applies to the _Live CD_ environment. I think Live CDs are quite important, and being able to type the @ character on a UK keyboard is quite important to us in the UK.

If a new user is taking Ubuntu for a spin, I think they'd really appreciate being prompted for a keyboard layout, perhaps at login time? Rather than discovering this later. I'd hate to find I had a working internet connection and browser, but not be able to type an email address, e.g. to log in to Google Mail.