Not sure I agree the logic that if its difficult to quantify, it means there is no benefit. Its difficult to quantify the value of good customer service also but that doesn't mean there is no value in it!
Good customer service can easily be quantified, a person whom has had a good experience is more likely to purchase from that company again, however the problem is that it doesn't work in reverse since people are creatures of habit, how many people say "I'll never fly Ryanair again" after a bad experience, only to then fly with Ryanair on their next holiday because of price factors alone?
In your service example, there are people employed by companies to determine exactly how good / bad their customer service can be before they don't make more money / lose more money. They could only get this balancing act right if customer service was quantifiable. It is the reason why Qantas (and numerous other companies) have a tiered customer service model, with access to certain levels based on your perceived value to the company (in QF's case, it is easy since each customer has an individually assigned status).
A genuine facebook "like" gives a brand a good indication of the number of people whom might consider purchasing from that company. But there are many cases of companies purchasing "likes" to simply pump up their own ego's. (Certain political parties are very guilty of this), and since a "like" takes virtually zero effort on behalf of the liker, it is not exactly a very good measure of a brands actual potential, and often the "like" is the result of the "liker" seeing one post which they enjoyed. How many facebook pages are there out there where the vast majority have "liked" the page, but the liker has zero intention of actually purchasing from that company? How many people actually go back and clear out their list of "liked" companies?
I'm not anti facebook as a communications medium. Personally I think social media is a really good communications medium for companies to interact with consumers and consumers to interact with companies. But just like with TV advertising where only a small percentage of viewers of your ad might actually do anything about it, a "like" really is nothing more than a viewer indicating to the company that they saw the companies TV advertisement and they thought it was amusing. How many amusing TV ad's are there which whilst you might enjoy, you have no intention of actually following up with the company?