As far as I can tell, there is no API (official or unofficial) to access information about Apps on the Android Market (info such as Title, Icon, Description, Downloads, Comm
Another option to capture data is using the tcpdump tool that comes with some custom images (like Cyanogenmod and others). You can capture all the packets and then analyze them using Wireshark. This route is easier than hijacking wifi.
Checkout this splendid posts to clear out some things:
Update I have been working on this a bit more and @gsmd is right and they use Protocol Buffers to transfer the information and with the technique described above you can capture the packets. Then you'll need to dig into protobuffers to understand the messages.