ADFS 3.0 Session Persistence

We've just completed an ADFS 2.0 to 3.0 cutover.  We now find that when logging into the ADFS URL and any Relying Party Trust sites, that once the browser is closed (any browser) the cookie is lost, and each time you open the browser you need to re-authenticate.  In ADFS 2.0, we did not see this behavior.  Microsoft is advising that adding the adfs page to IE Intranet zone will resolve (tested and works).  However, why was this not necessary in ADFS 2.0?  Are there any other settings that can be set so the cookies that are generated are Persistent, based on a TTL, instread of Browser Session Based cooklies?