Absolutely! it appears to be an issue that may be browser specific. Since I develop on both IPhones and Android I make sure to try my HTML5 apps on the default browsers (Safari and Android's webBrowser). My new IPhone 5S picks up the altitude just fine, but my Samsung Galaxy S4 continues to display "null". I built a native Android app version of my program to make sure it wasn't a device issue. It comes back with my altitude just fine. No answer, but still researching as altitude is important to us as well.
I also just verified using Chrome browser on same phone (S4); no altitude unless using my native app.