It's only really delayed sales for Apple, they know they'll get people buying the watch one way or their other. It's more of a gamble for EE I guess depending on how much they paid for exclusivity.
It will be one of those decisions where we'll never find out how it plays out for EE.
I think a good comparision is Kindle cellular. My understanding is Amazon don't charge the punter for data, its FREE.
This is how apple Watch 3 cellular should be, just like Kindle FREE.