Back in 1991 we moved to Germany with out 1986 Alfa 33 Green Cloverleaf.
Registration, with the V5 and CoC took about 30 mins at the local Vehicle Registration Office.
In 1999 we returned, with a 1997 Mercedes E200 Estate. Again registration here in the UK was painless, it was issued with an age related number plate.
In 2002 my pal Colin moved to Brussels for a 3 year posting. He took his UK specification BMW RT bike. Registration was a nightmare, involving BMW UK, BMW Munich and the BMW distributor in Belgium. The process took 6 months and cost 20% of the bike cost.
So why do some countries make such a fuss when others don't? In essence the EU Rules are the same, it is just local interpretation that varies...