They probably should but there are many providers (e.g. Softlayer) who, on the more expensive plans, will give you your own /28 or /29 for free without even asking if you need it. (Comcast and AT&T are also guilty of this on business tier cable/DSL plans.)

Linode is definitely the strictest in my experience when it comes to enforcing ARIN's rules (if HTTPS is your justification, Linode actually checks to make sure you're serving up a valid certificate). This is a good thing for the Internet but somewhat frustrating when other providers are so much laxer.

Or, viewed another way, it is evidence of Linode's attention to detail, which will help you many more times than it will hurt you.

Verizon handed me a /24 for a T1 line. No questions asked but that was 10 years ago :-)

I needed to fill out a form and list the use of each IP address before Comcast would give me a /29 and that was ~5 years.

Wow - about ~2 years ago we had to convince Comcast not to give us a /29! At least they could be convinced - AT&T couldn't.

Maybe it's just the luck of which rep sets up your account. I wouldn't presume that they ever look at the form or decline a request.