Hi Peter,
pages blocked by robots.txt would be considered to be not there, thus not flowing pagerank. You might want to use "noindex, follow" on these pages: pages are crawled and links on the page would be followed, by that any recieved linkjuice would flow from these pages to others. Noindex would mean that these pages wouldn't dilute PR (and ranking).
Furthermore is "noindex,follow" on a page to page basis faster and more secure keeping pages nonindexed than by robots.txt (which is only crawled every 12 hours or so).
You might want to use noindex,follow on all non-important pages such as legal etc.
Sebastian