The TK have always has some of the most powerful magic in the warhammer world. Everyone else was getting updates, why not TK? Also, as for thinking that bigger Bone giants would be better than a Sphinx, or a Legitimate sphinx?? (no idea what you mean) I have no idea what you mean. So the current line was better because it was the current line?
Also, remember that the studio painter CHOSE to paint them as having black onyx or whatever, you can easily paint it in another manner, make it look more stone or however you wish.
How are the snakes any more complicated than the scorps are? One 'works' the other doesn't? Doesn't make any sense. So maybe a unit here or there is not your cup of tea. My understanding is that core skeletons went down in price and TK chariots will be solid. So it will still keep the classic elements intact.
A. Here's what a more "legitimate" but still fantasy-appropriate sphinx would look like (to assist in your lack of imagination):
http://4.bp.blogspot.com/-BO5zSCZ7zDw/TXty_TQFZSI/AAAAAAAANsM/o6LN4W_W8h0/s400/Warhammer_Great_Sphinx_model.jpgB. Just repainting the model can't change the entire model's sculpt. Nor can a change of color alter the texture of the sculpt.
C. For you to call a model line "better" is highly dubious. The new line has a more diverse range of options, but lacks the condensed, stylistically sound approach the old range had.
C. Your argument against my opinion of the snake riders is pretty bad, both in concept and execution. There's a big difference between an animated statue that is mildly reminiscent of an Ushabti and a skeleton surfing on top of a fast-moving giant snake. A skeleton has been, and still is, described as clumsy, slow, and lacking in motor skills. They definitely shouldn't be able to ride anything like that. They could have themed them in a similar style to the Tomb Scorpion, but they didn't. They look radically different and pretty silly, where as the way they did the scorpion was both cool looking and functional.