I have little doubt that what a person has grown up with has a strong influence on what they find easiest to read. Do I like serif fonts on my ereader simply because I grew up reading serif fonts in books, or is there a genuine difference? Did past studies effectively control for that historical use aspect?
And screen quality (not just PPI, but contrast and all the rest of it) has made a big difference. The subtleties between different serif typefaces, or between different sans-serif typefaces, was often lost on older screens. Now you really can tell the difference between a period and a fly-spec ... well, most of the time.
There are still enough lower resolution displays that sans-serif is sometimes a better choice, especially if you like small text, but it's getting less common as a real requirement. However that doesn't change what people have grown accustomed to seeing on screens, so I think sans-serif is often chosen now as a matter of convention or habit rather than genuine need - particularly when you look at the font sizes used on many sites.