The Windows/Mac versions do not have in-app purchases, so the salaries are higher to make up for that difference. The iOS/Android/Kindle versions' salaries are lower because they can be supplemented with in-app purchases.

this is kinda embarissing, but what are in-app puchasec?

When you buy applications (apps) for devices like an iPad or Android tablet, you often start with a free "lite" version. Depending on the application, you can buy upgrades, full versions, power-ups, etc. for the app. The LDW games for devices (at least the ones I know of) are free as a "lite" version, then you buy game features using in-app purchases. The PC/Mac versions are purchased outright.

I didn't realize that about Day Traders' salaries, and find it highly amusing.

Ok, I'll try not to adopt day traders!