Your household insurance might well refuse to pay out if there isn't evidence of forced entry. That's a fairly sizeable variation in the cost of being broken into ...
Maybe, I probably wouldn't try to claim on the insurance though. My most expensive to replace thing is probably my cd collection, which as far as I'm aware thieves don't go for, my tv is small cheap and unbranded, my laptop is ancient and the battery is knackered. I suspect the most fence-able possession I've got is a Kitchenaid mixer.
The only reason I even have contents insurance is because it comes with the buildings insurance.
Ironically, perhaps, the case I was thinking of when I wrote the comment was my friend's insurance refusing to pay out on his CD collection being stolen because there was no sign of forced entry (he'd left the patio doors unlocked).
This was a number of years ago though, whether thieves still take CDs is an interesting question.
The only reason I even have contents insurance is because it comes with the buildings insurance.