DeltaNg,
There are a number of confusing elements in your statements and they need clarifying. The rules you are quoting are the operational rules and, as you have mentioned offshore, I make the assumption that you are referring to JAR-OPS 3.
Each State is responsible for its own compliance with ICAO Annex 2 (Rules of the Air) - the conditions under which IFR is specified and the low level rules are not necessarily the same in all European States; for this reason the operational rules do not (normally) prescribe an operating height - which might itself be in conflict with a State's Rules of the Air - instead specifying the minimum cloud ceiling.
Hence, for overwater flights JAR-OPS 3.465 stipulates a ceiling of 600ft by day and 1200ft by night. For flight between helidecks with a sector length of less than 10nm, there is an exception to this policy as shuttling is permitted at 300ft by day and 500ft by night (a Risk Assessed policy that has been the de facto standard in the North Sea for a number of years).
VRF flight without alternate fuel has always been permitted for return to land base where the destination is at or above VFR limits; however, a Risk Assessed policy has permitted an IFR return to base without alternate fuel when the conditions at the land base satisfy a number of mitigating conditions (minimum cloud base, location near to the coast, the presence of a low level route which can be flown VFR from the coast in the conditions specified, the presence of weather radar which permits a let-down over the sea to 500ft, etc).
The reason this alleviation was introduced was to prevent scud-running back to shore in conditions where IFR alternate fuel had been (legitimately) traded for payload. It is expected that such flights will be conducted IFR with an instrument approach at the destination.
Flights in limited icing conditions are undertaken with a not-dissimilar set of rules that have been in existence in the UK for a number of years and which are now being introduced into JAR-OPS 3. These flights in icing (and limited icing) conditions are conducted in cloud and under IFR.
Jim