Should I be compensated after completing my degree with my current employer?

Ive been employeed with a company for 12 years. I started as a temp hire but have since been promoted twice at the standard 10% rate. My last promotion was to supervisor 3 years ago putting me at 40k/yr. During the 3 year period i completed my BSBA degree. After researching, I discovered a supervisor 10 years ago started at 45k. He had a degree but no experience. I also learned average compensation based on my skills and education should be 50-55k. A new company offered me 58k in a different city. I gave my current employer the courtesy of trying to match and they said they dont pay employees based on degrees obtained after employment. My question is, is this standard business practice?