Mike,
There are not many inland waters over here that take more than 10 mins to cross!
No there is no such monitoring service over here, even for the longer crossings. You can talk to a variety of services depending on your crossing and flight rules but unless you call for help nowt will happen unless you are overdue (going to the continent) or someone rings in to tell them you are later than expected.
Going back to the comfort zone issue and the difference of its width depending on whether you are on your own or with family.
My family will be able to look after themselves pretty well I suspect even without my physical presence (especially under the guidance of my very able wife!) but I would feel terrible if they came with me and by a fluke, I would be the only one to survive without them.
The issues about abilty to egress, what do you let yourself into, what do you expose yourself to seem to explain that difference quite well for me.
FD