The update that describes why 4KB of RAM was necessary was interesting to me. In 1998 I wrote a Java Virtual Machine in assembly language for a PIC-like microcontroller that only had 4k of ROM (actually it was 4k instructions, but they were 12-bit words giving 6kB). I managed to get all of the important features of the language to fit, including exception handling and an interactive debugger. However by the end, each time I wanted to add a new instruction to my code I had to find something else to optimize first so it would still fit in 4k.
By the end I convinced myself that 4k was the minimum possible code size for implementing a JVM.
The JVM was used in the Parallax Javelin Stamp - a Java version of the BASIC Stamp (http://en.wikipedia.org/wiki/BASIC_Stamp).
As an aside, the SX microcontroller only had 256 bytes (yes bytes!) of RAM internally so I used an external 32kB SRAM for the Java heap and stack. The 256 bytes of internal RAM held the internal state of the interpreter and memory manager.