Not hugely cheaper, more like £1,000-1,500. There are big gaps between the specs (£2,500 between Explore and Excite, £2,000 from Excite to Exclusive) that could be narrowed a bit and maybe the two lower specs could have a few more toys (no satnav on the mid-level one?).
Going above £20,000 is a psychological thing, maybe it's deliberate as they want to take MG into new territory but I think places it as steeply priced in some people's minds where £19,995 isn't even though it really isn't that big a difference. As it is, people will look at what else they can get and where budget or smaller crossovers (Ssangyong Tivoli, Dacia, Suzuki Vitara etc) are priced.