This is where you are mistaken. Those models are indeed
re-based. Compare the the pictures in the cabinets to the ones in our current army book. They are the exact same ones. The Troglodon, the blue Stegadon, the Terradons and the Bastiladon are the exact same models as found in our book.
The best give away is the Bastiladon: not only are the colours exactly the same, but the markings on the shell are precisely identical. The snakes are painted in the exact same colours in the exact same sequence. Please take a very close look at it, page 71 of our army book. There are only two possible explanations for this...
- They gave the artists the original models and instructed them to paint new ones that are 100% identical down to the smallest details and then provided them with the instruction to base them on rounds.
- The artists were instructed to re-base the original models.
The odds of #1 being true are so remote that it is mind boggling. There would be absolutely no reason for GW to do this. They are a business, everything they get their artists to do is done with the intention of making money. Why would they re-base (or even worse replicate a former paint job) for no other reason than "aesthetics".
To answer your question directly, GW would not create something for purely aesthetic reasons because it makes no financial sense. It costs them money (paying their artists for their time) to do so and they stand to gain nothing. Trust me, GW had their artists re-base those models for a very specific reason. I guarantee you that those models will be used for photographic purposes to support GW's new project. Odds are that project is 9th edition (and this is where the personal estimation comes in) but I must concede that the possibility exists that it is instead an offshoot of some kind.