K28 vs K28r...what is the difference?
 

Anyone know the difference between the K28 and K28r, if any?

I am guessing you are talking about Kinesis wheels? It is my understanding that the R version has a slightly larger center that removes the step in the lip, making the lip flat/smooth from the edge all the way to the wheel center.

Yes, they are the Kenesis wheels. I think your assessment is correct according to a poster on Rennlist. Someone mentioned that water traps in the perimeter of the wheel on the flat "R"s creating an unbalace of wheel weight at speed.
Luckily, my car does not do too much rain duty.
Thanks!