"No" is the accurate single word answer but also a misleading one. The loader is the only attachment I can think of that would usually be the same brand as the tractor. Even that is not always true because there are several 3rd party loaders made like Bush Hog, Quicke, etc. Your question begs a question: What attachments?
Anything that fits a 3pt hitch (which is a very large and varied market!) can be had to fit the standardized Deere 3pt from umpteen sources other than Deere. The loader came to mind immediately at your question because Deere has hung on way too long failing to put skid-steer compatible quick attach (SSQA) points for buckets, etc, on their loaders.
Now back to the technically correct answer to your question: It depends. Some items (take a rotary cutter for example) are generally more expensive if made by JD. But even that is not always true as Bush Hog and some others do make rotary cutters more pricey than Deere. Deere's corp thinks they are more expensive so much so that they encourage and support their dealers carrying a lower priced Frontier line of green attachments. Deere was hurting trying to compete or you would never have seen Frontier stuff on their lots. So it depends, and that's why I asked "What attachments?"