The main reason not to measure smokeless by volume is accuracy. If I am using regular black powder or pyrodex and set my powder measure at 100gr I can mistakenly set the measure off one or to gr above or below that figure and not change the pressure placed on my rifle much. Do the same with smokeless setting your measure at 43gr of 4227. If you are off by 2gr of powder you still can have a safe load, but the percentage of change to your charge has been increased or decreaed more than double what the charge for large volume powders is.
I'll admit that there are times it would sure be nice not to have to deal with the hassles that come with traditional powder. My biggest fear is that some fools will get themselves killed. I'm not blaming Savage for the actions of stupid people. My problem is the way some people will interpret the recomended loads for the savage. Take the 43gr of 4227. Savage recommends the max load of black powder for their rifle is 150gr. They also recommend several loads of smokeless. Someone, somewhere will take this info and conclude that these two powders are equal and load a traditional muzzeloader with 43gr 4227. Then their heirs will sue both Savage and Knight, T/C, CVA or whoever. Win or lose, the cost of doing business just went up and my next rifle will cost more.