I don't disagree with your line of thinking. However:
Also, even if the control group had a reduction of 15%, the result is treported that the treatment reduced relapses by 30%
I don't think that is quite right. For instance, in the trials for Copaxone, the Copaxone group had 29% fewer relapses relative to the placebo group (1.19 relapses/year for the Cop group vs. 1.68/year for the placebo group). http://tinyurl.com/ykwv34y
Other trials have different endpoints (disability progression, # of new lesions, etc)., but they are usually given relative to the control group.
But when you talk about whether the treatment will help one person, those variables are important. For example, if a treatment says that relapses were reduced by 30%, you don't know if everyone had a reduction of 30% or if half had no reduction and the other half had a reduction of 60% (unless they include this analysis in the work-up).
This is very true, but I think some of this depends on the primary endpoints of the study. Some are more valuable than others, in my opinion. For example, some trials use the number of patients who are relapse free after a certain period of time. I think this is a better indicator of how individual patients might fare on the treatment. And even if they aren't part of the primary endpoints, some studies may report on individual patient statistics (again, see the Copaxone trial).
If it is properly designed, I think a CCSVI trial could provide valuable data on how much the treatment helps. Reports are Zamboni has already done just that, so, like everyone else, I eagerly await his paper. Of course, I can understand that waiting for further trials will take time that many MS'ers don't have.