A 90km/h speed limit for HGVs is by no means universal in Europe. In fact, fewer have a 90km/h limit than those which have an 80km/h one.
The following countries have an 80km/h (or lower) limit:
Austria
Czech Republic
Denmark (if over 3.5 tonnes or towing trailer)
Finland
Germany
Greece (70km/h when towing a trailer)
Ireland
Italy (if over 12 tonnes or towing a trailer)
Croatia
Lithuania (if over 7.5 tonnes or towing trailer)
Macedonia
Netherlands
Norway
Poland
Portugal (if over 3.5 tonnes and towing trailer)
Switzerland
Sweden
Serbia
Slovakia
Slovenia
In practice, however, most trucks and caravans on German autobahns seem to travel at around 90km/h. Speeds are usually only monitored where signposted 80km/h or lower limits apply, such as road works, etc. The police don't normally intervene in sections which are not limited unless there is a gross violation or the outfit appears to be obviously unsafe.
Overtaking restrictions for HGVs do not automatically apply to private cars towing caravans, only when specifically signposted to cover all trailer units.