Actually when I googled about this matter, I read some topics where women told about rectam exame being performed by their gynos, these results were in Portuguese (pages of my country, Brazil), that's why I thought it was common, it was like 3 out of 4 girls telling that they've already had rectal touch during their gynos appointments. Maybe I got unlucky to find untrustful results or gynos behavior in Brazil are different than other countries.
Talking about the ultrassound, I understood what you said, but don't you think the pelvic exam became "unnecessary", considering the ultrassound is capable of covering even a larger area and provide a clearer result?