Our name is only three letters, so it makes for a very easy lockup, and I believe it's strong without any symbols. I wouldn't call this the best approach in every case, but it's what we prefer: http://tsrgames.com/
A symbol alone as a logo is good for an iconic brand, but not necessarily for a brand trying to establish themselves. A logo + symbol can work when that logo adds something to the meaning, like Amazon's smile mark or the Salesforce cloud. And sometimes the logo alone is stronger, like Google or IBM.
Wordless logos are as old as advertising. Car companies have relied on their symbols to speak for them for decades, and it's easy to think of classic symbols like the Playboy bunny, Penguin books, Swiss army knives, etc. that have been wordless most all of their lives. Apple's logo has been used without words right back to the 1970s.
There will always be different approaches that work for different brands. Choosing the right approach for any company is always on a case-by-case basis.