I can sympathize with the point you are making. No one can really predict the future, so your opinion may be vindicated. Google beat out every search engine, so who knows.

However, a few counter-points:

1) Brand value is critical. Look at Coke and Pepsi. Anyone can create a cola competitor, but no one can conceivably do better than these two. On internet properties, brand value is still important. Look at Priceline.com and Expedia. They still worth billions.

2) AirBnB has operational expertise that no one else has, in large part because they've been solving this problem w/ more funds and more man-hours than all of their competitors combined. More operational expertise = better service = beats out competition.

3) AirBnB is capitalized enough to buy out start-up competitors. Right now, most investors doubt someone can take on AirBnB. As such, most investors will push founders to go for an exit whenever possible.