Re: industry subpar knock-offs
You need a 64-bit CPU to access more than 3 gigabytes of RAM, though (same as with a PC), and modern smartphones are right up around that mark.
You need a 64-bit CPU to provide more than 2 gigabytes of virtual memory to applications (anywhere between 2 and 4GB, depends on the operating system and its configuration, but 2GB is typical because it's trivial to separate user and system space).
ARM's ARMv7A architecture supports Large Physical Address Extensions, which permit a 32-bit processor to manage a 40-bit address space - up to 1TB of RAM. ARM first implemented this in the Cortex-A15 core. It's up to the OS to map the app's virtual memory to whatever regions of physical memory are required.
All current phone/tablet operating systems restrict the amount of memory that an app is permitted to use. iOS does not have published limits but reportedly the iPhone 5 will close your app if you allocate more than 645MB of its 1GB RAM. Android has an OEM-configurable maximum heap size - you can request a 'large heap' which gives a higher limit to your app, but this is still dependent on the OEM and is well short of the total memory available. Windows Phone 8.1 allows apps designed for 8.1 up to 185 MB for phones with less than 1GB of RAM, 390 MB for 1GB devices and 825 MB for 2GB devices. I believe these limits are relatively low so that several apps can remain in memory at once.