Just because you repeat something multiple times does not make it true.
In America, at least, pilots are required to wear their seatbelts at all times while at their stations:
http://www.risingup.com/fars/view_far.php?part=125&type=FAR&num=311
I'd be rather surprised if Europe didn't have similar rules.
Rules are one thing. Everyday work is another one.
It might sound offensive, and while this place here is not an aviation forum anyway, but there is a huge difference between being forum/internet-theorist (or "defender of the truth"

) quoting rules and posting papers and graphics all day long (or calculating how much turns/degrees it needs to change an altitude setting on the FCU via the corresponding knob on an Airbus) or being practically involved in the corresponding real life business day-to-day.
And sorry that I just have to repeat it once again, but pilots are
not wearing their seat belts
all the time, especially not during cruise but already not during climb as long as there is no turbulence. And this is also the case in the US and elsewhere on the globe. Rules aside. There are no traffic tickets and no police airplanes. And besides, it's not convenient to wear belts all the time especially on long-haul flights. Just as it's not convenient to leave the seat in the position you chose for take off and landing all the time. During cruise, while there is no turbulence: pilots unbuckle their seat belts usually, pilots adjust their sets for more comfortable positions, and some even doff their shoes and use the foot rests shoeless for more comfort. Also, they put their food/trays/cups/salad bowls everywhere in the cockpit, even on top of knobs on the center panel (I have seen it many times). Rules are one thing, comfort/everyday work is another one. And not to mention the use of cell phones. Passengers would be just envious...
No belts US:
http://www.youtube.com/watch?feature=player_detailpage&v=0Vmg_kAD1EQ#t=29
No belts Germany/Europe:
http://www.youtube.com/watch?feature=player_detailpage&v=nhXXjNybx6A#t=726
No belts Russia:
http://www.youtube.com/watch?feature=player_detailpage&v=be120hZLS8o#t=2463
Same applies for the "two person rule" by the way (rule being different from everyday work and certain airplane types). But it's hard to find video evidence of pilots leaving and entering the cockpit. Most of the time there is no one filming it (and no one controlling it and distributing traffic tickets anyway). And same applies for medical checks as well for example. There are tons of rules and obligations in aviation, but also lots of pilots who don't care all the time. Don't expect that not informing the airline or flight physician about each and every health issue is just an isolated case. Neither at the big airlines, less than ever at smaller airlines. That's not any different to other jobs. You don't want to lose your job, less than ever your licence, as long as you can avoid it and not threatening safety.
In Germany it's not allowed (anymore) to visit the cockpit in flight (just as it is the case in the US as well). But I know very well how a jump seat feels in flight. Even when the pilot is having a leak and returns with some sweets for the co-pilot and the lucky flight deck visitor.
Just don't stick to legislative texts too much.