I've heard a lot of these things before, too, and the thing is they're both true and false. It depends, you see. Getting a great review from Publishers Weekly or a major publication does help; sometimes a little, sometimes more.
Paid advertising can help, if it's a small amount to a target audience.
FB and Twitter still help me sell books, although I've never sold in huge quantities anyway, but when one of my books is on sale, and I tell people about it, there are more sales.
And yes, things have change a heck of a lot in five years since I self-published Fatal Encyrption in 2008. FB and Twitter will further decrease in usefulness and maybe something new will come along, or Amazon will bring out a whole new publishing/selling option.
Those who wrote about realistic expectations are right on the money. Back in 2009, over a 1 million books worldwide were published every year, according to Bowkers and other sources. Can you imagine how many more are out there since then? What I've really noticed over the past 2 years is the huge numbers of free books. Honestly, you could fill your Kindle with freebies and never have to pay a dime to read, and maybe that's the scariest part for me.