If I had to roll up data from 200+ devices, I'd use a Redis database (http://redis.io) to receive and stage the data. Then it's easy to write small programs that can grab the data from the database and format it for spreadsheet and web display.
Any database would work, of course. But if you go the Ethernet route, you can use the (free) Bitlash Redis client to make the Arduino part of the problem very simple. Count pulses, report up the line to the server every N seconds. It's a couple of lines of Bitlash. This approach reduces the software problem to database reporting and format conversion.
Be sure to get a big bottle of aspirin for the practical problems that go with managing so many devices. Consider staging a small pilot project with just one arduino, and then scale it to a dozen machines before you rewire the whole factory...
-br
Redis: http://redis.io
Bitlash: http://bitlash.net
Bitlash redis client: bitlash/BitlashRedisClient.pde at master · billroy/bitlash · GitHub