I admit that I'm not entirely certain what to think about hearing "Koi no Mikuru Densetsu" as played by the Tokyo Philharmonic Orchestra.
There's something strangely compelling about listening to pop music, as in popular music that is of interest to the teeming masses, as played by an orchestra. Or a full choir chanting something vaguely Latinesque, going "Requiem aeternam dona eis, Domine" or "Rex tremendae majestatis" or "Agnus Dei, qui tollis peccata mundi" and so on to the tune, because apparently Mozart's Requiem Mass in D minor is just about the only piece of music in Latin many popular composers are willing to make use of.
That might be a bit unfair, of course. We've got our own example of an alternative, Mahler's Symphony No. 8 ("Veni, creator spiritus, mentes tuorum visita") in the sixth chronological episode of The Melancholy of Haruhi Suzumiya, and occasionally composers make up their own ("Cum historia mutat valde, Razgriz revelat ipsum primum daemon scelestus est"). But I digress.
Part of it might be the sheer effort required in getting all these people together, in a setting normally expected to be a stuffy, bourgeois concert hall, performing with great pomp and professionalism something that was originally sung (badly) in MIDI by a combat waitress from the future in a bunnysuit. The incongruity makes such an arrangement unlikely, which is why it is so fascinating when it actually happens.