The answer is in the question: presumably the parameters of the Si4735(-D60) were even worse to use it alone for a AM/SSB receiver. Still, it is seamingly worth to be used as an intelligent, programmable and cheap stereo FM/RDS receiver with some extras, plus an AM IF receiver/demodulator.
Originally, Si4735 is an AM/FM receiver, it is only hacked by writing a third-party firmware to work on SSB as well lately, analog filtering and perhaps a better than 1 kHz tuning resolution might be the reason to the 909 has got a superheterodyne unit before the Si circuit.
AFAIK, even the pin number 1 is wrong on the drawing, it should be the pin 2. :-)
Several years before I have built a nice receiver using this IC, I still have the video of it, but I cannot tell you how good it can be on AM, it was only tried on my bench in the middle of a city, surrounded by thick, RF blocking walls and steel and glass buildings... Anyway, it has dealt with the usual enormous domestic RF noises well, and it was sensitive at least on FM.