Whether logging is on by default depends on the device type or application. The logging needs to go somewhere (it's almost never stored on the device), like a syslog server. And then you need to have sufficient storage on that server. If you have a busy site, you can be talking many TB or even PB a year and that requires a SAN/NAS. Thus many service providers skimp on implementation.
Both in Canada and the US there are laws as to how long and what types of data a service provider must store. But the Internet and service providers evolve so quickly that the laws can't keep up. Whereas a ISP must keep email logs and connection logs for a minimum of 6 months (made that number up, the duration has a formula), there are no specific laws for VPN services (yet).
But keep in mind, under the old Patriot Act (I forgot the new name and too lazy to Google now) certain LE agencies can go into a provider RIGHT NOW and ask for logs and/or set-up mirroring in the name of "prevention of terrorism". No formal court subpoena required. How they use that information in court is a different issue. So using VPN services will still help <-- this is partly why Fuji keeps stressing US VPNs vs off-shore VPNs. Also this is why a lot of websites (including TERB) are no longer choosing to be hosted in the US or Canada.
You will also notice allot of web sites have gone from HTTP to HTTPS (like TERB). This means the actual content between your browser and the web server is encrypted end-to-end - so if someone is monitoring/logging/mirroring your ISP router, they will know you are surfing TERB, but will NOT know what is being transmitted.
I don't think that's the main reason LE would be monitoring. Possible scenarios:
1) Suppose a SP is found to be underage. LE could scour the sex-board sites for anyone who has reviewed the SP and press charges.
2) If an SP gets hurt or killed, LE may scour the boards for customers in the last 0-90 days as part of the investigation
3) If the site gets hacked, the hacker could post all the IP addresses and Email addresses on the net. After the Ashley Madison leak, I'll bet 2/3 the wives in NA used the search engine site to look for their husbands Email or home IP address. I know several companies in Toronto I worked with did a search on their public IP address ranges.
4) If the info was made public domain, I know allot of HR departments who search for this kind of info as part of their hiring process. It's not an easy process and in many case the info is useless, but I'll bet $100 dollars that 10-30% of people use their work address or full name in gmail/hotmail email address on the porn sites. Dummies! Also we all have political enemies and any bad information is useful information.
Good post, thank you.