High School Musical/WMG

All of the musical numbers are real.
In the world of High School Musical, breaking into spontaneous, well-choreographed song and dance numbers is part of puberty, just like acne, voice changes, and the realisation that sex might be awesome. This explains even the anti-singing characters (such as Chad) breaking into song unexpectedly, and why none of the adults sing. The adults either have a Weirdness Censor that makes them ignore the kids' performances, or just politely avoid calling attention to it, much as one wouldn't mention a teenager's acne. The kids who deride Troy and Gabriella for sacrificing their other interests for singing just think that it's embarrassing, because it's calling attention to aspects of teenager-hood that everyone just wants to ignore.
 * So the "High School Musical" in the third movie was the equivalent of a theater instructor in our world putting on a show called "Senior Year: Tampons and Wet Dreams"? Darbus is edgy.
 * More like "Senior Year: Zits and Dandruff." Still gross but not as risque.
 * This troper cannot, will not, and has not been able to take teenagers randomly breaking out into song and dance in a movie seriously EVER AGAIN. Because she always thinks of this entry and it is now her headcanon!

The films were intended as a parody.
They were going to be an loving parody of tween-Disney, with all the random moments,bad acting, bad effects, bad singing the works. However, an excecutive worked out the how MUCH they could make from this and all of the parody was removed.
 * So they ended up with a coherent plot, good acting, and good singing?

The emcee is God.
As suggested at the Agony Booth. Now the coincidence at the beginning of the film makes perfect sense. Why God is bothering with tween romance, on the other hand, is beyond me.

Troy's story is based on Brian Thompson
Actor pretending to want to be a pro athlete?

Ryan and Sharpay were inspired by Jesse and James.
Just imagine them as friends rather than siblings living in the Pokémon world.

Ryan is gay, but he's not in the closet.
Many assume Transparent Closet. However, he isn't in the closet. It just never comes up in conversation during the movie. Judging by the way he dresses, he's comfortable enough to have come to terms with it, so he doesn't feel the need to talk to somebody about it, and for reasons unknown, he might just not be interested in a relationship (or could be the only out kid at his high school).

Ryan is bisexual.
He's a really, really femme guy, but that has nothing to do with his orientation. This is why he's able to have so much Ho Yay with Chad while also being in relationships with Martha and Kelsi.
 * Martha?
 * In the second movie, while Kelsi was still being put together with Jason, during the dance numbers that required couples, Ryan danced with Martha or Sharpay. YMMV on how much of a couple this made them.