Lumping in cross-dressers and run-of-the-mill gender variance denies this very real condition the attention it deserves, it reduces it to a choice. There is nothing wrong with the choice, and people should have the right to express their gender however they choose, I just think that we need to be careful about maintaining a separation between gender dysphoria and gender variance.
On the actual question at hand, clinical intake studies have been pretty consistent in this regard. The number of people who have gender dysphoria that becomes severe enough to prompt treatment (in western European countries) is about 1:10000 (for transgender women) and 1:27000 (for transgender men). (Judge, Ciaran, Claire O'Donovan, and Donal O'Shea. "Gender dysphoria-prevalence and co-morbidities in an Irish adult population." Neuroendocrine Science 5 (2014): 87)
That being said it is difficult to estimate the number of individuals with gender dysphoria who choose not to seek treatment (or those who choose to self medicate). People like John are unfortunate, and a hopefully the bi-product of an age we are on our way out of. That being said, John is clearly not transgender, they may suffer from gender dysphoria, but they are not transgender.
Today we have a much better understanding of gender dysphoria and have a number of long term studies which show hormonal and surgical transitioning to be an effective treatment (e.g Gorin-Lazard, A., Baumstarck, K., Boyer, L., Maquigneau, A., Gebleux, S., Penochet, J.-C., Pringuey, D., Albarel, F., Morange, I., Loundou, A., Berbis, J., Auquier, P., Lançon, C. and Bonierbale, M. (2012), Is Hormonal Therapy Associated with Better Quality of Life in Transsexuals? A Cross-Sectional Study. Journal of Sexual Medicine, 9: 531–541. doi: 10.1111/j.1743-6109.2011.02564.x). I
“First you ask about what sex is on your birth certificate. Then later in the survey you ask, ‘What is your gender?’? - This, of course, doesn't work in first-world countries where gender dysphoria is treated like an intersex condition and the individuals are free to amend their birth certificates.