Without meaning to diminish the seriousness of these crimes; there are two things to consider, when comparing international crime statistics:
1. Differences in reporting rates.
2. Differences in definitions (”sexual assault” covers a lot more ground than “rape”).
“Without meaning to diminish the seriousness of these crimes...”
Trying to differentiate between rapes and sexual assaults in a discussion does appear to be an attempt to diminish the seriousness of these crimes. Both crimes are very serious in nature.