Brian,
I've been using RS for nearly two years now, and your question was practically the first one I had as well.
The bottom line answer is usually "no". HTML, the format rendered when viewing the RS reports online, is really a visual medium, not a print one. MS uses a downloaded control to render a report from the HTML (you can find this control, called RSClientPrintClass, in IE: Tools > Internet Options > Settings > View Objects).
PDF doesn't render the report HTML same way as RSClientPrintClass. Ergo, the differences you see.
Best,
Craig