No it's not true.
The drive MUST be formatted as FAT32 to be used on both. But there are inherant limits to FAT32 (4GB max file size). And Windows won't format a drive as FAT32 above the size of 32GB as an artifical force to move to NTFS. However, you can format it on OS X no problem.
Beyond that, nothing except Windows can write to NTFS, so you don't want that format for use on a Mac too.
A Windows box cannot read/write to a HFS+ disk (the Mac format) unless you buy 3rd party software (MacDrive).