Hi Roger,
Don't know about the UK, but 1-2 years or so ago there was legislation passed in the US that required insurance companies to offer the insurance. Most likely it was legislated because they were not going to do so as evidenced by the lobbying that occurred.
The wording of the law here is that in order to pay out on a terrorism claim the act itself had to be a certified act of terrorism carried out by a foreign terrorist group--this certification is an government duty here.
By way of example, the World Trade center would have been covered, but the bombing in the federal center in Oklahoma years ago would not have as it was considered an act of domestic terrorism.
So in the US, though I think the ins. companies are glad to receive premiums for the insurance, they would rather not have to offer it. One act like the WTC every decade and they'll all go broke.
So, to reply to your rhetorical question, yep, it's a sign of the times.