North Americans are said to average 10-12k per year which would put the time interval around 12.5 years. Time and environment are very important factors for belts. Not sure why our owner/service manuals overlooked specifying that. Even if the belts have a high silicon content, the hotter running engines (for emissions purposes) will serve to offset some of those gains.
I'd rather trust the EU's spec, which doesn't overlook the obviously important and go with the 125k/10y interval.
I believe we have had some members who were changing out on that 150k without issue though.