Exactly. I did the same for a conference, which I was paying for myself. Exhaustive research into airfares revealed that while there were fares that looked less expensive at first, once you added in all the taxes and whatnot, they were more expensive than the train.

Also, the experience was so much better. Easy to deal with luggage. Enough room to actually get work done on my laptop. Easy to get to the conference location once I got to Brussels, which was a couple metro stops from Brussels Zuid. Plus, it only took 2 hours--from where I was staying in London, I could eat half that time just getting to Heathrow.