Perhaps he was tuning with injector timing which would be more complicatd because he would need to make a MAP compensation table. With VE, it's no more complicated than tuning with MAP because you're doing the same exact thing. The TPS table might take a little longer to make though because RPM has a greater effect on VE with TPS than with MAP. VE is pretty much linear with MAP but the relationship between TPS and VE is less clear.
Here's a pretty standard VE table using MAP as the load:
Notice that it's pretty much a linear gradient from left to right since VE primarily changes with MAP, not RPM.
Now here's a TPS map:
Notice now there are two gradients, left to right with throttle position and top to bottom with RPM. This is because the relationship for VE is dependent upon both. We can relate this back to MAP easily.
Think of it this way; VE is nearly linear with MAP, so if we can find a way to relate throttle position to MAP, that relation will then have a linear relation to VE. The problem is that throttle position is not the only thing that determines manifold pressure, RPM does too. At 1000RPM it might only take 10% throttle to reach atmospheric pressure but at 8000RPM, the engine is drawing in much more air and has a much greater potential to make vacuum so more throttle is needed to equalize that vacuum to atmosphere. This is known as "effective WOT" and is why when looking at the TPS table the VE at 40% throttle and 9000RPM is equal to the VE at 6% throttle and 1000RPM. Theoretically, given the load on the engine, these two points will have similar manfold pressure because of VE's direction relationship with pressure. But load is not always the same because the car will be driven in different gears and on different inclines. These load changes will show up as differences in manifold pressure and is the reason why MAP compensation is needed if not tuning with VE which already does MAP compensation automatically.
Furthermore, VE tuning with TPS as the load should theoretically provide a superior tune than with MAP as the load if done properly. The reason is simply because it is accounting for more vaiables, making it a more complete tune. With TPS VE you're including TPS, MAP and RPM but with MAP VE you are missing TPS as part of the equation and relying on the fact that VE is more related to MAP than anything else and dropping off TPS as a variable because its significance is less. It also makes tuning for transient throttle enrichment easier since throttle changes will instantly be recognized as a load increase and enrichment will happen mostly automatically.
I hope that wasn't too complicated for everyone!