I read here that Microsoft makes $5 to $15 on every Android device sold because Android can read the FAT filesystem. Ubuntu can also read the FAT filesystem but no payment history to Microsoft exists. What is the difference?
This is more of an issue with exFAT, not FAT.
One of the notable benefits of exFAT over FAT is its support for individual files larger than 4GB, an essential feature for video recording applications.
The most notable drawback, obviously, is its proprietary nature, giving a Microsoft tax to every device that implements the standard. It is an essential part of the SDXC standard, meaning that devices that support SD cards over 32GB have to pay money to Microsoft.
Edit: after reading the actual article, I realise now that the article itself suggests that vendors are paying to use even FAT (not exFAT). Sorry for assuming that was your own confusion.
However, the point muru made in his answer still stands: the free software implementations of FAT (including the implementation in Linux, the kernel used in Android) are not subject to Microsoft patents because they don't implement the patented algorithm for maintaining long filenames and 8/3 letter filenames side by side.
The article even admits it can only speculate, and I'd have to guess that it would be wrong about vendors paying royalties for the FAT filesystem for the above reasons. However, that's a financial decision that's up to the vendors - it's possible that there are other considerations at play.
More specifically, the