The fare from anywhere in the UK by Eurostar to Brussels is, in fact, less than the fare to 'Any Belgian Station', but only by a few pounds.
Since Eurostar has moved to St Pancras, it is much more attractive to potential northern fliers, as it taps the market from the East Midlands and Sheffield (trains arrive the same station); Leeds and Newcastle (5 mins walk from Kings X); and Birmingham and the North-West (10 mins tube from Euston).
It also arrives an Brussels South station, which, though not ideal, is a great deal more central than Zaventem. It is supposed to be a pig to get on the bus from Charleroi to Brussels, and the more civilised alternative by taking a local bus and a train takes a while.
Oostende airport is not in the centre of Oostende, so that's another bus ride.
My favorite airport in Europe, Antwerpen, is too near to Zaventem to attract enough flights except for London City.
So it's Eurostar to Belgium - and it's not that bad at all!