i2c sensors straight to USB

This may be hopelessly naive, but it seems sometimes like I am just using my arduino as a universal adaptor.

Is it possible to wire an i2c sensor direct to a USB serial and control it from the giant micro-contoller that is my laptop?

I know you can buy special adaptors for i2c communication.. is it just that the arduino is so cheap and flexible compared to these?

Is it possible to wire an i2c sensor direct to a USB serial and control it from the giant micro-contoller that is my laptop?

Yes, through an adapter (you allready found out)

is it just that the arduino is so cheap and flexible compared to these?

Think so,

But you could build your own, e.g. based upon a 168P ? or - http://www.instructables.com/id/Worlds-Cheapest-I2C-I-Squared-C-Adapter/step5/Software-and-Projects/ -

Cheapest one I found - http://www.ebay.com/itm/USB-I2C-Serial-converter-data-port-Arduino-/230667782820 -