Are Transvestites Always Homosexual?

No.  Transvestitism has nothing to do with being a homosexual, this is a common error.  Transvestitism is about being more comfortable dressing as a woman than as a man.  
If we take the comedian Eddie Izzard, he describes himself as a male tomboy.  It's nothing to do with his sexuality, he just likes make up and eye liner.  Enjoying dressing as the opposite sex is about filling a gap within one self that is not a sexual fulfilment.

Far more drag questions are homosexuals, but this does not mean that all Drag Queens are homosexuals either.  The problem with this kind of question is that it seeks to narrowly define human behaviour into a neat category, and that is rarely possible, especially with human sexuality.  Do men always like blondes? Do women always prefer men with muscles?

I know where you are coming from, and there is much confusion generally in this area.