I think you forgot about three other major stumbling blocks to using open source. 1) IT Resistance - most IT departments are wedded to Microsoft products. It is what they know. They don't have any experience or background in Linux or using Open Source software. They will fight tooth and nail to stay in their comfort zone.
I recognize this resistance to change and here's what I've got to say about it: Why do we push teachers to jump into the 21st century, but we don't require it of our tech folks? I realize there are many many tech folks out there working in schools to do great things and to utilize the resources of Open Source, Web 2.0, and Social Tech. But what about all the folks who are beholden to MS Office? I say just as we make it an expectation that teachers will integrate current tech into their teaching, we should also make it an expectation that tech officers will integrate new thinking about open solutions into their work. And there's always another way to change this paradigm: make your tech hires based upon the candidates' proficiencies with Open Source and Social Tech; change the culture by changing your hiring qualifications.
2) Licensing - many Open Source or "free" software products are only open and free to the general public. Institutions, even public ones like schools, are expected to license the software just like Microsoft's stuff. It may be cheaper, but it is not always free as in free beer.
I understand that this is often the case, so it's important to tread carefully and to know exactly what it is that you need and want from the tech you are seeking. At my school, we recently encountered a situation where it looks like we're not going to be able to support MS SharePoint as we've done for the last several years. What to do? Well, chances are we're going to go with Google Apps for Education which is totally free. The package includes email, sites, and all the office-style programs we could want; so why pay good money for the MS alternative? (I've used Google Apps exclusively over the last few years for office, presentation, and archiving, but this would be my first foray into using it school-wide. I'd love to hear from some folks who have about the pros and cons of their experience.)
3) Training - just like the IT dept., the faculty and staff of a school district is already heavily invested in using Microsoft products. They have probably even had training from their school district in Office, etc. Few teachers will want to repeat that with "new" software packages. And going back to #1, it is the IT dept. that will have to develop the training, since there are few ready to go, off the shelf resources for Open Source.
I've heard this argument three times in the last four days. I think one of the nice things about many open platforms is the ease-of-use. Nobody who's ever used MS Office is really going to have a problem using Open Office or Google Docs. Nobody (I'm talking amateurs like me and most of my teacher friends) who's tried to create a web page using Dreamweaver will balk at using a free drag-and-drop program like Weebly to create a class page. There's really very little 'training' in anything a teacher would ever need to do in a classroom. Instead of 'training', try modeling a few uses of Google Earth, or Jing, or Diigo to your teachers and then let them decide how and what they'd like to experiment with.
Maybe I missed a memo, but it really doesn't seem all that hard.