As far as why someone would not like to include the philosophy, may I pose a supposed answer?
I have trained under an instructor that did not use traditional Aikido philosophy. He actually integrated Christian teachings into our lessons, but that's a different subject. Anyway, I do not agree with many eastern philosophies, ie good and evil are equal, balancing forces. Because you contain a concept of good and evil, you have proven that good is more powerful (C.S. Lewis, 'Mere Christianity'), but once again, that's a different subject. So, it was necessary for me to find an instructor (forgive me if I do not address him as sensei, he wouldn't appreciate that) that agreed with those things I've found to be true. As for whether you can obtain the level of ability without the philosophy as you could with it, I don't know, but I'll be proud if I'm ever half the Martial Artist my instructor is.