The windows version will be available this month for $730, with other versions (including a $600 version) coming in May. The SteamOS version is coming in May for $500. I'm guessing the $600 windows version and $500 SteamOS version are basically the same hardware specs.
Windows charges different license fees depending on how powerful a device is. Gaming hardware will have a more expensive license fee than a lower power device.
Honestly when you have devices like the steam deck targeting $400 starting price, paying up to $100 for a windows key is pretty significant.
I hope for their sake their other Legion products are better than the Legion Dual phone I have, because it constantly reboots for no reason, has no way to remove bloatware, and has no control for when or if the fans turn on, they seemingly turn on for no reason, even when the device is not in use.
I wonder if Lenovo gets a revenue share when they sell a game on the device. This could also explain the $100 price difference as the they are counting on the additional income. Are there any leaks / rumors on this?