First of all, I couldn't help but laugh when I realized that nopony's actually ever started a thread about this until now! Kudos!
Second, I do actually think that friendship is actual magic in the show, and I'll provide an explanation as to why in the space below with a response from an earlier thread I'd made that focused more on the importance of friendship in Equestria's history.
Explanation:
This realization in turn led me to re-evaluate the importance of friendship in the show itself, and develop a second point that made me realize even more than I had previously that "MLP" is a fantastically well-written and very smart show. As I previously stated, "Hearth's Warming Eve" teaches the ponies and, in turn, the audience, that the foundation upon which all order and harmony in Equestria rests is friendship. This, although maybe not apparent at first glance, considering the first 1 1/2 seasons had already dwelt upon the magic of friendship extensively, lifts the importance of friendship in the show itself to a whole new level!!! Before, we'd seen that friendship was simply the binding element between the Mane Six, and while certainly a powerful element, in that through its power they were able to wield the Elements of Harmony, its relevance was relegated to the present. "Hearth's Warming Eve," however, showed that throughout history and in all times, past, present, and future, friendship had been, is, and always will be the binding element upon which all harmony and order in Equestrian society is established! Friendship, essentially, allows Equestria to be what Plato in his "Republic" calls the "best city". First of all, in "The Republic," Socrates defines justice as people minding their own business, literally, each person sticking to doing what they do best, to the benefit of themselves and society. Prior to Equestria's founding, while the three races of ponies certainly stuck to their tasks, they only did it for themselves, and only cooperated with each other at the bare minimum out of the utmost necessity. It could not be said that they had one "city" even (i.e. one society); they all had their own distinct cultures and societies. The pegasi were essentially timocrats in that they placed the greatest value on honor and martial glory, the unicorns were more or less oligarchs with their love of wealth, riches, and gems, despite their access to great knowledge as well, and the earth ponies were basically (degenerated) democrats (in the sense of the classical definition of democracy) in that they placed a great deal of value on equality (more so than freedom, and as such were all equally poor) and clearly had elected representatives (i.e. Chancellor Puddinghead... like I said, degenerated democracy. HA! ). However, after the events of the first Hearth's Warming Eve, all three races, due to friendship, truly united and established one society in Equestria, a society where each and everypony does whatever they are best at, mind's their own business, and as a result, both the individual and society are benefitted. This is justice according to Plato and Socrates! Furthermore, it can also be said that in many ways Celestia and Luna are essentially the guardians, or philosopher kings (rather philosopher queens), that Socrates speaks of in "The Republic" as well, for while they certainly allow each and everypony to mind their own business, their own business appears to be ruling the state on account of their wisdom, for they have made their business knowing truth and knowledge, which is the business of the philosopher. In Equestria, logically, the highest knowledge and truth must surely be that which has to do with the magic of friendship, since that is the very foundation of Equestrian society, and who other than Celestia and Luna have been shown to have greater knowledge of the magic of friendship? Therefore, it can be accurately stated that, due to knowledge of friendship, along with all other things, Celestia and Luna are Equestria's philosopher queens, and in conclusion, friendship as the theme of "MLP: FiM" is even more important to this show than I even previously thought it was!!! Seriously, when I came to these conclusions, my mind was blown away!!!