Denying any responsibility for this is: David Morgan-Mar
The author writes:
It's important that you, dear reader, recognise the makes and models of the eight cars in the background, as this provides a significant clue to accessing the secret URL where all of last year's Shadow Reality strips can be found. These strips are bonus content which explain the reasons why Roxanne went off taco salad for the past few months, as well as the whereabouts of Steve's brother-in-law Albert's wife Amanda's dragon.
If you can't work out the makes of all the cars... well, then, I guess you'll never know. I did test this on Susan, and she correctly identified three of the eight when I showed her the comic at web resolution. Given she's only a second year apprentice auto mechanic, I feel confident that most of you will be able to solve the puzzle.