I don't operate the 737 or fly out of LTN, however a number of factors might effect the apparent speed of the aircraft.
Quite often ATC give the instruction "no speed" on the departure. Some operators prefer to maintain 250 knots max. below FL100, in case of bird strikes, for pax comfort and to keep noise levels lower (both in and outside the aircraft).
EZY, I imagine, are always in a hurry if that terrible docu-soap was anything to go by, and I'm sure that they wind the speed up as soon as possible (mind you so do I!!)
Paintjobs and size of aircraft can also play tricks on the eye. Watch a jumbo jet coming into land, it looks slower than a turboprop. I can assure you it isn't!!
To conclude, I'd suggest there is no difference between the 737 operators departure speed, unless BWL has a particular SOP below 10,000 ft.
Hope this helps!
