Papering over a binary blob

When you want a chip that is available and reasonably priced in small volumes and also does everything that you want (I believe the one chip in GTA-04 does Wifi, Bluetooth, and GPS), then your options are limited.
I am certain the GTA-04 developers only chose a chip with closed firmware because there was no other option at a comparable price/functionality/availability point.

Of course if you know of a better device and can get a competitive quote for small quantity, I'm sure the developers would be very interested.

Building a fully open device that is so expensive that only a couple of people will buy it is not good business sense.