Currently, Canvas and Sakai are the only LMSs reviewed which has somesupport for xAPI (emphasis on some). Blackboard, D2L, Sakai and Canvas all have support for IMS Caliper, a more edu specific format.
Without getting into turf wars, xAPI is generally very popular in training, CMS, and informal learning spaces. IMS Caliper is a little later out of the gate so it's not fair to generalize it's adoption, however it was worked on in conjunction with LMS partners and the IMS consortium so it will most likely have greater adoption in Higher ed.
So why this whole course about xAPI then? Well, more of the world's population and systems will be impacted or integrate with xAPI due to it's adoption outside the walled gardens. It's popularity in the CMS / training space is not to be discounted as we currently see more 3rd parties adopting xAPI then Caliper.
The other important note is that there are conversations between the two communities for ways to generate translation layers that can convert statements from one format to the other.