I call shenanigans. Either you're trolling me or trying to screw with me... or both. Since we're talking Java and OSs, try this. Install 64-bit Java and only 64-bit Java (remove all other Java versions). After install, a web page appears asking you to verify the Java version. If you have a 64-bit browser, you'll see the version you just installed. If you have a 32-bit browser... I'll leave that as the exercise. If I get it right, below will be the answer wrapped in a spolier.
<spoiler>
According to the above, due to 64-bit being backwards-compatible or defaulting to 32-bit, you'd expect the 32-bit browser to also show you the Java version you'd just installed, right? And you'd be wrong. What the browser would actually detect/show would be that you had no version of Java installed or none the browser could detect. Now, install the 32-bit Java and the version checker automagically works.
</spoiler>
Experience is my source. I seem to recall lots of chatter when Windows released their first 64-bit OS because no one could use some/most/any of their 32-bit applications, even with an OS-encoded 32-bit shell environment for backwards compatibility.
I appreciate your volunteer efforts. I do not appreciate misleading instructions or erroneous informations, and will call you on such.
Suffice to say the instructions above should have been amended to say something along these lines...
To permit the FTB launcher to access more than 1GB RAM, you need to be running a 64-bit OS and you need to install the 64-bit version of Java. Uninstalling the 32-bit version is not required.
If you'd like to keep the 32-bit version of Java installed, or you need the 32-bit version [browser-dependancies, etc,] make sure to install the 64-bit version into a different location.