Well, it's also, I suspect, heavily dependent on the ship you're in and your combat rating.
I almost never get interdicted in my Asp, and have never been interdicted in my Vulture (although it's early days). My combat rating is expert.
I was flying an empty taxi Sidewinder with no cargo hold and no weapons (to get to my other ship) last night; I was interdicted twice. Think about it - what would you interdict: the flying tank from Mars (with 4 burst lasers, two multicannons and an A5 shield), a flying death machine from another dimension (with class 3 pulse lasers, no cargo, and an A5 shield), or a piddly Sidewinder with no guns? You can't cargo scan in supercruise, btw. Pay attention to the system security level too - it does make a difference.
In that regard, I find the AI to do a fair enough job. Forgive me if I sound unsympathetic, but it's because you're easy prey. The reason AI programmers turn to probabilistic algorithms is because even rather simple ones do a convincing enough job. Suck it up and get out the small ship and get something with a bit more firepower. Do some RES hunting to improve your combat ranking (and make yourself a fat wad of cash - bounty-hunting has received a buff). You'll notice a difference eventually.