"It is for a jury to determine infringement based on the legal definitions determined at a Markman hearing."

Markman hearings were brought about because jurys made up of the general population have to deal, sometimes, with complicated engineering and technical issues that they are more than likely unable to comprehend. So, the Judge determines these issues at the Markman hearing and how they pertain to the law.Then if the case goes to trial instructs the jury at trial regarding these issues. So, in a sense the Judge determines infringement, but the jury has to rule on it with his instruction. You are right in that the Jury has the final say.