The benefits of Excel over Earls Court that no one seems to mention are:
1. Excel has waterfront access (kinda handy for a boat show
2. Excel is considerably newer
3. Excel has better transport links (City Airport, DLR, close to North Circular, close to M25, M11)
4. Excel has better parking facilities
5. Excel has purpose built accomodation next door (Marriot and Ibis)
It may be a pain to get to for those of you on the south coast, but I'd imagine that the main benefit to those who actually show at the event, is that the group of people with the largest disposable income in Europe is right next door in Docklands, with the City only an extra 15 minutes away. They can literally go to the show over lunch.