Looks like on 2.4 you were creating a character device with a major
number of 253 and, then, on 2.6 that changed to a major number of 252.
According to the "devices.txt" file in /usr/src/linux/Documentation, those number fall into the range, well, here's what's in the file:
240-254 char LOCAL/EXPERIMENTAL USE
240-254 block LOCAL/EXPERIMENTAL USE
Allocated for local/experimental use. For devices not
assigned official numbers, these ranges should be
used in order to avoid conflicting with future assignments.
You have to contact Matrox to find out why they changed major numbers. Perhaps they found that some other popular device manufacturer was using 252 under 2.6 before they got their driver ported/updated. Kinda hard to say why they changed it. Pity they didn't update their documentation/tutorial. Or, if that's a third-party tutorial, then that author never got it updated in time.