Okay, so cribbing numbers from wikipedia, Develop mag, and actual dev websites, we can actually get a decent(ish) number for Nintendo's R&D...
- Nintendo (NCL): 1,400
- Mario Club: 250
- HAL Laboratory: 137
- Intelligent Systems: 123
- Monolith Soft: 83
- Creatures Inc.: 82
- Retro Studios: 80
- Nintendo Software Technology: 80
- Genius Sonority: 60
- Game Freak: 57
- Project Sora: 30
- Brownie Brown: 27
- Noise: 21
- TOTAL: 2,430
... this is missing Ambrella (small dev, probably 30 or less) and Silicon Knights (Nintendo technically still holds a 30% stake in them, but whatevs).