I'll tell you what I see in my business (I operate a blowing company):
For most jobs over 10 yards, look at getting a blowing company to do the job. Many landscapers think that every job over 5 yards should be blown in, but in truth (at least in my area), jobs under 10 yards are not profitable for the blowing company. A lot depends on how the job is laid out (big mulch beds much better than a bunch of tree rings for the blower).
As far as a markup the landscaper charges, I find that most of my clients have in the neighborhood of 20~30% markup from what I charge. Some of this markup is taken up by prep work the landscaper does before the mulch is laid (i.e., trenching, cleaning up debris, etc.). But, take into account that we can generally do the same job at 10~15% less mulch than you can do by hand - again, a lot of this depends on how the job is laid out and how well it has been prepped out.
I try to explain to my landscaper clients that they should view us as another tool to use, not a complete replacement of their existing methods (i.e., by hand). I like to use analogies to further explain this concept: When a painter buys an air gun to speed up time to paint a house, you do not expect them to throw away all of their paint brushes. Some areas are best done by the air gun, some with paint brushes. The same concept is directly related to blowing mulch. A lot of jobs are best done by the blower company, but there are some jobs that are best done (both aesthetically and financially) done by hand. Small, intricate beds with a lot of annuals and tree rings are two examples of jobs that are best done by hand.
I hope I explained this well to everyone.