I'd say that that was fairly standard - in fact almost universal until fairly recently. Nowadays, some motor insurers will include comprehensive cover for a certain period in the price quoted, but they usually make a point of saying so, particularly because it's not standard. And that's only been fairly common in the last 10-15 years anyway.
I don't remember the details on this, but I'm fairly sure that if you go back say 30-40 years, UK motor insurance didn't automatically provide any cover outside the UK, and you always had to pay for an extension ("get a green card"), and in some cases get special documents (eg a bail bond if you were driving in Spain, as the police there tended to impound your car if you were involved in an accident until they'd investigated it). Then something (premumably EU-related) changed and third part cover was automatically included, but usually no more. The reasoning was that driving abroad (unfamiliar road rules, especially driving on the right) meant extra risks that it wasn't fair to spread over everybody's premiums when relatively few people incurred the risk. As it's become more common for Brits to take their cars abroad, some but not all companies have built the cover into their standard policies.
If you intend driving your car abroad , it's worth comparing the costs and terms for doing so when you buy your insurance - it may be OK paying the extra per trip with your current insurer, but you may well find it's better to select one that automatically includes comprehensive cover in the basic premium as it can work out cheaper. But also take note of the way it works which can vary between companies - some say you're covered for x days in a year and don't need to tell them when you go (good for spontaneous last-minute trips), but others want to be informed of dates each time you travel (to tally the days you've used presumably) otherwise you won't be covered even though it's included in your premium.
