Here's an interview with a woman who got uber drivers prosecuted: http://www.bbc.co.uk/programmes/b0783lhl
Here's another article about the same woman: http://metro.co.uk/2016/04/19/blind-woman-repeatedly-turned-...
A different case: http://www.bbc.co.uk/news/uk-england-birmingham-30523449
And another: http://metro.co.uk/2011/02/28/blind-yvonne-saint-john-guide-...
Uber is far from unique in refusing service dogs or wheelchairs. It seems the rules are more clearly explained to regulated taxis than they are to less regulated minicabs.