The pose is not absolutely inaccurate. If a theropod with a long tail like that were to rear upwards, its tail would naturally angle down towards the ground, where the tail tip would touch. Like someone else said, that pose would probably be uncomfortable and the dinosaur would not be able to hold it, but its certainly possible and therefor not inaccurate.
I will always love tripod over biped. Bipeds are often given ugly oversized feet to help them stand. Sometimes the figure won't stand anyway due to the legs being warped, which happens very easily. Bipeds are also not very nice from a play-perspective. A biped will not stand up on carpet even if it is very stable on a flat surface. Tripods on the other hand, will usually stand even if the legs are warped. They will stand on carpets, uneven surfaces, and non-level surfaces, which even the most well-made bipeds cannot do. Unlike a biped, they wont topple over at the slightest bump. My bipeds are always falling and knocking over the dinosaurs next to them. The few bipeds I own will live out most of their life laying on their sides, or leaning against a quadruped so they don't fall over and hurt themselves or others.
Regarding the concav, I wrote this on DTF: "I think the concav is beautiful, and I dont mind the tripod stance, but I am now officially VERY tired of that overall pose: standing still, head lifted, tilted to one side, mouth gaping. Why not try closing the mouth? Putting the head down? Changing the position of the legs?"
Regarding the concav's tripod stance, I personally prefer tripods the way battat made them, by bending the end of the tail sharply down. I know THIS was inaccurate in real dinosaurs unless the tail was broken, but it allows the toy dinosaur to resume a more natural horizontal body position. If the bent tail is enough of a problem for someone, they can easy straiten it with hot water. Oversized feet (like with the safari acro) or oddly angled bodies (like with this carnegie concav) are both difficult or impossible to fix.