Maths and NVR have been proven to be linked - so if you are strong in maths you are likely to be strong in NVR too. And, as has been said, NVR is the one are that cuts out all language bias. However, as NVR and Maths are linked, the equal third weighting that Bham/Warks used to have, was actually favouring mathematicians. Ability in English has also been proven to link strongly to ability in all other subjects (even science/maths questions require an understanding of English to understand the question) with essays etc and all GCSE exams have the warning on the front about the need to use good English.
The change was therefore to reflect the need for a good level of English as being a better indicator of overall intelligence and ability in all subjects - nothing to do with race or ethnic mix - there are threads on this every year...
KCG - I take your point that Maths and NVR are pretty much linked, hence the reason to weigh them on par with English. But I would argue that English is something that can quite easily be learnt over few years, but not sure if it's the same with innate ability. I hardly knew any English when I landed in this country, but it only took me few years to satisfactorily start communicating with people. Having said that my grammatical skills are still quite poor and love using an exclamation everywhere