He means RMC are using topper exclusively for their own ground up creations, and doing all conversions with I box only. I don't think this is it though. As I understand RMC don't want to do regular wooden track replacements anymore (which used to be one of their main activities before the conversion craze I think) and focus on making their own coaster, ground up or conversions.
Anyway, if a park offer them a big juicy comtract for a conversion, bit require a topper instead of I-box or the deal is off, I'm sure they'll accept. I-bix or Topper, it doesn't change much on their end.