Bob and I have had this discussion off line, but I'll post it here for the benefit of others.
Although I've been a recumbent rider for 20 years or so, I never measured with my recumbent. As a two-wheel bike recumbents tend to follow a somewhat crooked path, not good for measuring. And, a three-wheel recumbent, although tracking straighter, probably wouldn't get close enough to a curb to meet the 30 cm requirement.
I suspect that the wobble is due to balance although in all the time I've been riding, I don't really feel out of balance. It's not a huge wobble, but it must be noticeable enough that when riding on a road with traffic, cars tend to give me a wide berth. Perhaps they're afraid that I'll fall over in front of them.
There are different types of recumbents. Mine has under-seat steering and a short wheelbase (the crank is in front of the front wheel and the handle bars are beneath the seat). I suspect that a long wheelbase version or one with above-seat steering would wobble less. I also expect that viewing the counter could be a problem on either version.
Also, the action of your legs is very much the same as on an upright bike, but with the added stress of poor hill climbing capability.
Ron