It's been my experience that "twin" sized beds in Japanese hotels are quite a bit bigger than what we would call "twin" here in the US. How wide/long are they exactly?
I think you'll find this chart of bed sizes to be just what you need.
- North America: 39in × 75in (0.99 m × 1.91 m)
- Japan: 38in × 77in (0.97 m × 1.95 m)
Which would seem to indicate you're perhaps mistaken in your experience, unless they have a different custom size that you've been experiencing.