This IMO is not entirely accurate. It is still happening to a significant degree, its just that the initial strong percentage gains often (not always) happen between Christmas and New years day now.
Its true that MANY people expect it to happen, but this is why they have adjusted their entry timing to December, to get a head start.
One of my big wins shot from .0003 to about .02 between 12/25 - 1/1, then peaked at .05 in January... The run was still nice in January (100%+) but if you bought end of December, the gain was 15,000%... This is the difference a little timing can make.