Patents ignored or Patent Loopholes?

It's not just 'wanting to patent', its also about proving to the USPTO that your invention has not been shown/patented before (Prior Art) and is not obvious. The idea 'per se' is probably not patentable ("I'll rent you a room/give you a ride"), but there are probably a lot of details about how their system manages loads, etc., that are.

BTW, AirBnB has five published patent applications, so they did try...:-)

LuF

As Luis mentions, AirBnb did indeed start filing patents in 2012 and has as of today 5 filings still in the pending phase. Please see: http://worldwide.espacenet.com/searchResults?submitted=true&locale=en_EP&DB=EPODOC&ST=advanced&TI=&AB=&PN=&AP=&PR=&PD=&PA=airbnb&IN=&CPC=&IC=
It can take 3-4 years until a patent is granted depending on the industry. I am not touching here on the actual patentability of apps and software as such, which others here will be better qualified to answer, but see below.

Uber has filed at least 26 patent applications. Please see http://worldwide.espacenet.com/searchResults?submitted=true&locale=en_EP&DB=EPODOC&ST=advanced&TI=&AB=&PN=&AP=&PR=&PD=&PA=uber+technologies+inc&IN=&CPC=&IC=. Their main focus seems to be on "Location Based Systems" acting in concert with their app. It may be that, given their first-mover posture and their status as a lighting rod for criticism, Uber was strongly incentivized to create a strong patent portfolio to help establish their number one position in the apps driven transportation business and to protect their de facto and de jure ‘monopoly’ position.

Where companies don’t dilgently apply for patents, e.g. Wimdu (vs. AirBnB) and Lyft (vs. Uber), it can be that their strategy is more focused on becoming an acquisition target and they actively choose not to expend resources in protecting their technology. In some cases (as happened with Twitter/IBM), successful tech companies that do make the distance with few or no patents of their own eventually enter licensing deals with more established companies. Whether such a strategy is deliberate or a consequence of a lack of planning early on, it does highlight the need for a well-thought-out IP strategy.

One other factor worth mentioning here is the United States Supreme Court's 2014 decision in the Alice Corp. v. CLS Bank case. This decision had the practical effect of making it almost impossible to get a business method patent, and very, very difficult to get software patents. Consequently thousands of business method and software patents granted over the past 15 years have become worthless because they are unenforceable. This is now another wrinkle to consider in properly working out the IP strategy of an internet startup.