You're not necessarily wrong (that a ton of modules will be downloaded) but there are two points worth mentioning.

1) you can install from cache with something like:

  npm install --cache-min 9999999

2) npm's infrastructure has scaled extremely well. Gone are the days of spotty uptime and slow resolution. I maintain an npm proxy for one of—if not the—single largest consumer of npm modules and other than the very occasional 502 blip, npm has been rock-solid.