As someone who worked in ecommerce doing £400k in 2 years, what a load of crap.
If ecommerce sites are "demoted" in serps it's because:
- duplicate content - they run the standard product descriptions from the suppliers, the same as 99% of people selling the same product.
- thin content - a lot of suppliers don't actually supply descriptions/images. If all you have is a title and a price you're probably not going to rank for anything and if you have 50k products it's unrealistic to manually add this.
- poor site structure - SOOOOOOO many ecommerce software packages are total crap. You can have 15+ urls for the same products (depending on category they are in, variations, dates, even updating prices can give a new URL in some cases).
There is no evidence Google force people to buy adwords to do well at ecommerce, please don't spread false information.