Pretty much every uni does accept BTEC for at least 1 subject, the only one that doesn't is Imperial College.
Even Oxford and Cambridge accept BTEC for subjects like Engineering, Art and Computer Science.
I think BTEC is excellent, but I agree it should not be accepted for every subject. If someone wants to study History at uni then they should know they need to take History A level to meet the prerequisites, BTECs are only offered as vocational subjects so really you should only be going to uni to study something in the area that your BTEC is in, unless you take a foundation year.
Most unis will accept BTEC for subjects like: Business, Engineering, Computer Science/IT, Media, Nursing/Health Sciences and most Science degrees accept the Applied Science BTEC however some will ask for certain units to be taken (e.g. at least 6 Biology related modules if applying for a BSc Biology degree) which is fair enough. And a lot of units bow accept the Applied Law BTEC for entry onto an LLB.
BTECs are great if you know you want to go into a certain area after leaving school and probably provide better preparation than taking potentially 2 A levels unrelated to the degree you end up doing (for those who take 3 A levels).
I did an IT/Computing BTEC and have just started my MSc at a top 10 uni and some of the content in my MSc modules I previously did on my BTEC 5/6 years ago, which works out great for me as I have specialised in the field since I was 16 and not changed my route, for those who do change their mind it can be quite difficult as generally have to attempt to get into something that they're not qualified for and then if successful catch up to get to the level their need should have already been at.