Your description was still inaccurate, and I've explained what does cause the reduced overall data usage on a Blackberry.
Didn't say you were wrong about that. I acknowledged those reasons for overall lower data usage. It's just that web and other such transactions, and their compression, have nothing to do with the thread topic, which is involuntary data usage.
My description was targeted toward this thread topic and specific posts in this thread, which were about whether or not all phones constantly use data for push.
And the answer still is, a Blackberry doesn't have to constantly use data and battery for keeping a RIM server push connection open, as other phones must.
OTOH, a typical Exchange push user can easily eat up 5-10MB a month just on server pings. In which case, just turning push on will account for 100% of data usage... without actually reading any mail or doing any browsing.
And that's what's important for the OP to know.