I used Xlibris initially when I started self publishing. When looking at Ingram Spark a while back I saw a lot of similarities with Xlibris.
One thing I was not so sure about was if Ingram Spark advertises and sells your book in their own online store.
Part of the contract with Xlibris is that for some indefinable time(depending on how well your work sells and whether it eventually gets picked up by a real publisher)they advertise and sell your book through their book store.
The big difference is: if you intend on making a fair amount on your work you have to overprice the book both for expanded distribution and limited distribution because{at least in the case of Xlibris)they want to extract the same supposed costs of offering your book that the major book outlets charge..
In KDP you get the same increase in cost with the expanded distribution because all of those outlets need to have the added insurance of a specific percentage income to even think about taking a risk and even then they can refuse to carry your work for any number of reasons--one of those being if you chose not to allow returns[allowing customer returns can be dicey since the cost of that falls back on the author].
So for the expanded distribution I'd characterize it as being very much the same. It really probably doesn't make a difference unless for some reason you gain a tremendous following and people everywhere want your books. In that extreme case you might begin to sell more through that distribution than you would through Amazon alone. At that point you would want to get the maximum coverage. As it is, though, Amazon has quite a wide world wide distribution on it's own.
However, with KDP you will always make much more of a personal percentage on what Amazon sells than you might make from the inhouse sales of other on line services such as Xlibris and what is necessary to satisfy the expanded distribution outlets.
So the distribution channels are very much the same though for self published books it is still up to individual outlets as to whether they even want to handle your book; though if you meet most of the minimal specifications for quality they will in general accept the POD(Print On Demand)books.
Plus now that KDP offers a hardcover option it makes your decision easier since doing everything within the same web app makes the whole process easy.
In the end none of these methods allows your books to be available in the brick and mortar stores--only on-line stores.