Yes, it's true.It doesn't NEED an onboard CPU to work on the 3DS
The only real reason for the presence of CPU (historically) is the GBA emulation and problematic somes games (opera browser, Pokemon for example)
You can not use the RAM without CPU.
Remember: in 2004 Nintendo released the DS with a GB / GBA port which enabled emulation with a linker slot2
2008: Nintendo announces a third version of the Nintendo DS, DSi without slot2.
Goodbye GB (A) emulation, goodbye Guitar hero who had left some months ago, goodbye Opera and pokemon.
it's a good metaphor but don't forget that originally ALL R4i, R4SDHC, R4GoesToTheBeach Deluxe ... are fakes, clones and imitation of R4 whose production has ceased around years 2007/2008/2009just look at the R4i Gold's many hardware revisions.