I've got an s22 with a single axle. Don;t know whether they pulled the old switch-a-roo on me before I bought it. I guess they could have, but the boat fits pefectly on it. I worried about the same thing, but it seems they built the single axle with HUGE wheel bearings compared to the tandem ones. At least Pete's trailer has different bearing than mine. The wheels are bigger, too, I think, since the single axle has 6 lug wheels compated to 5 on the tandem.
I've had one blowout in 3 years, and that was because the stem rotted. When it blew I barely felt it and the trailer did not do anything crazy like sway wildly.