The desire to totally own something can be expensive. I offer customers a 33% discount when they hire me for either Free Software (GPL) or Open Source (MIT, BSD, Apache, etc.) licensed projects. In addition to that savings, development time on GPL projects is almost always shorter because existing GPL software can be used. Also, with open source projects there is always at least some chance that other users will contribute useful code back to you (*).
I have talked to several of my customers at length on this issue. Most simply want to totally own the rights to what they pay for - no argument from me if that is what people want. Still, I think that many customers overate the value of keeping software that they fund proprietary: it is a "big world" out there and any small company is likely to have a huge number of competitors in their product and/or service space. For some projects, it makes sense to me to cut infrastructure software costs "to the bone", go open source, and try to compete for customers based on service. The risk of competitors taking away some business in many cases is less than the risk of spending too much money to get the infrastructure software that you need for your business.
(*) About 8 years ago, when I bought my first digital camera (wow, 320x200 pixels!), I faced the problem of storing and accessing thousands of vacation and family pictures. My solution was to 'scratch an itch' and write the PicWeb Java utility that would recursively scan directory structures and generate thumbnail images and an index.html file in each directory that would link to the index.html files in all subdirectories and all image files in the current directory. Really a simple program, but I had over 40,000 downloads from my web site over the years. The great thing was that 4 or 5 people made huge improvements to the functionality of PicWeb and for the slight cost of folding their code changes back into my codebase, I got the advantage of all of their improvements (as did everyone else). BTW, PicWeb was certified by Sun as a "100% Java" product and for that they sent me a free leather jacket with a giant embossed Java logo on the back. Still one of my favorite jackets. (Sun also waved the $1000 "100% Java" certification fee for both PicWeb and another open source project that I had, the NLBean).