The R3 and the S3 were the R & S pro team frames for a while, now it's the R5 and S5. The equivalent to the S2 was kind of the RS, which is now discontinued. So it looks to me like they've jazzed up the S2 a bit to replace the hole left in the range by the S3. It sort of makes sense but it's confusing because the number designations don't really match up, whereas the frameset prices for R3 & S3 and R5 & S5 were always comparable; you just chose between lighter weight or more aeros.
tl;dr: in the past, the R3 was always a more expensive frame than the S2.
The R3 and the S3 were the R & S pro team frames for a while, now it's the R5 and S5. The equivalent to the S2 was kind of the RS, which is now discontinued. So it looks to me like they've jazzed up the S2 a bit to replace the hole left in the range by the S3. It sort of makes sense but it's confusing because the number designations don't really match up, whereas the frameset prices for R3 & S3 and R5 & S5 were always comparable; you just chose between lighter weight or more aeros.
tl;dr: in the past, the R3 was always a more expensive frame than the S2.