There is no reason a market 1 exchange will not go beyond 4Meg, people can still sync at 8128Kbps and get good throughput. Distance to the exchange is key.
10% not get braodband from traditional methods, never believe the headlines, more like 99% can get broadband, but yes around 10 to 14% can only connect at under 2 Mbps.
That said other than money there is no reason someone cannot have Gigabit already in the UK.