Well, the first issue is that there are no large-scale commercial Thorium reactors, which means alot of actual design and running flaws aren't known yet - PWR a

Well, the first issue is that there are no large-scale commercial Thorium reactors, which means alot of actual design and running flaws aren't known yet - PWR and BWR designs are an old, tested technology with it's flaws widely known and compesated (even through accidents like TMI). However the biggest problem with Thorium MSRs is the political issue - MSRs produce Plutionum as a side-effect, which means Thorium power-plants produce nuclear WMD materials while operating. You can't do that with PWR/BWR designs, which is one of the reasons for their popularity - companies can export those reactors without fear of countries using them for WMD production.