That I agree, LiveView allows better manual focusing. The question is how often do you do manual focusing ?
If you had to do it a majority of the times, then there is something wrong with the camera. The manufacturer put in plenty of electronics ie. Contrast Detect, Phase Detect focusing to help you so that manual focusing is not required.
Also in a lot of dynamic situations, manual focusing is too slow. So only a small percentage of the time, you need manual focusing.
The point is, LiveView is good for manual focusing, which is used only for a small percentage of the time. That to me, is a definition of a nice to have feature (or not required feature), and it adds costs to the product.
Same with light meters. If people started using light meters heavily in their DSLR, what is the point of all that electronic sensors in the camera for metering ie. matrix metering, spot, center metering with xx number of metering sensors.