Journal length limits are partially responsible for the culture of bad writing in academic biology, but it cannot explain why most of my colleagues in biology could not express technical ideas clearly in writing even without length limits.
If you go to the older literature you will find papers much clearer than any biology talk I've heard. Arthur Koch's papers on cell shape are good examples. There was also a culture of monographs that is missing today. The best examples I can think of off the top of my head are one by Henrici (http://www.archive.org/details/morphologicvaria00henr) and Schrodinger's 'What is life?'(whatislife.stanford.edu/LoCo_files/What-is-Life.pdf ) are the two examples that occur to me off the top of my head, or Chargaff's scientific essays in 'Heraclitean Fire'.
Disclaimer: I loathe the culture of academic biology and believe that most of its practitioners should be defunded in favor of serious biological research.