Since no one seems to know, I'll have a wild guess;
Since "working time" isn't defined you might want to have a look at how it's defined for road transportation. Directive 2002/15/EC Article 3 defines "working time":
http://europa.eu.int/smartapi/cgi/sga_doc?smartapi!celexplus!prod!DocNumber&lg=en&type_doc=Directive&an_doc=20 02&nu_doc=15
If you're cleaning your boss' car at your workplace you're ready to take up normal work and this time should count towards the working time. However, if your boss on forehand tells you to continue cleaning the car even if the weather clears up, that time should not count since your work is unrelated to what's covered by the directive. If you're sent home on "stand-by", this time should count towards the maximum 2000 h "as determined by the applicable law". This means that it probably does if you're in Scandinavia.
"Would a fixed annual roster pushed right to the edge of the 2000 hours make it illegal to do overtime ?"
Isn't that the spirit of the regulation? However, there's a possibility for the appropriate authority to grant an operator the right to deviate from the regulation. The request to do so would probably be looked at more favourably if it's countersigned by the employee or its representative.