isn't the 45mb the size of the original "patch" update, but the latest one closer to 76mb or so?
I don't honestly know - it seems like people are reporting both file sizes. I do know that supposedly, the 45mb file is sort of like a "service pack" where only files that have changed are included.
The 76mb one supposedly contains a zip of the entire /system folder.
I am uncertain how VZW/Moto are determining which download each individual phone requires. But I suspect it has something to do with whether or not the person is running the official ESE81 2.1 build to start with. I believe the 45mb patch is ONLY ESE81-->FRG01B and the 76mb patch will take ANY version up to FRG01B.