Mauddib you are reading an awful lot into the situation that was never suggested by the OP!
Something that has occurred to me, though, is whether your DIL's parents are in a different financial situation from you? Is she concerned that one set of her children's grandparents will be giving more than the other, and not wanting to cause awkwardness?
If that is the case, it is a bit of a minefield. On the one hand, there is no reason why you shouldn't be able to give the sort of present you would like to; but on the other, it would be a shame if the other grandparents felt embarrassed as a result (or it could be the other way round - this is blind conjecture on my part!)
Again, the answer could be to keep Christmas low key, and do your own thing on the children's birthdays, when you are less likely to be compared with the other grandparents.