Albion College Astronomy Professor Nicolle Zellner says the move was made because a growing number of masses in space were fitting the same description as Pluto. So, either they make them all planets (which there may be thousands of), or they redefine what constitutes a planet... which no longer includes Pluto.
Pluto is now a 'dwarf planet.' The biggest factor in the new title for Pluto is it's orbit. It's on on the same geometric plane as the other planets. Instead, it's orbit is askew of the others.
A problem could arise in text books, especially as students are buying those books getting ready for the new term.
But, Dr. Zellner says most text books have been demoting Pluto anyway... which merits for being called a planet have been in question since it's discovery in 1030.