I'd say 95% of all applications use horizontal labels. 4.9% use vertical labels, 0.1% use rotation by some odd angle. So, 95% of all labels worked correctly before the change, additional 4.9% will work correctly after the change, 0.1% will have to think about the origin at which they have to place the label. Why bloat TLabel with another property which is probably for 0.1% of all users, and this only if they don't think.

The person who brought this up, uses vertical labels, he can anchor the labels to the pins of his Integrated Circuit image, and the labels will remain there on all platforms and for all form sizes. So he will be happy.