Do most people include ebikes on their home contents insurance? Does this normally cover thefts away from the home? Or is there specific insurance policies for bikes?
Yes, it covers thefts away from home IFF you meet the insurance rules, which normally require the bike to be locked to an immovable object. Sometimes with some particular category of lock ('sold secure gold or better').
What it doesn't cover is your liabilities if you run into someone or something and injure or damage it/ them. For that join the cycle club scheme, or get specialist cover.
There is an upper limit in most cases. Nationwide House cover has a £5k limit.