Or simply a fact of not knowing the rules?

I fly on ID-tickets a lot to SIN, sometimes via BKK, from Europe.

One thing I've noticed more and more during my trips there is that in Europe the airlines will put you in any seat that's still available on the plane. Ticket and check-in agents also tell you if economy is full but there are seats availble up front.

But in Asia upgrading ID-travellers doesn't seem to exist. If they don't have economy seats they won't let you on the flight...
And this has been on airlines like LH, OS, BA, QF, KL that normally when going the other way have no problems putting you in either business or first.

Anyone have similar experiences or know the resons for it being like this?