Smith has been with the Chiefs since 2007 yet has ended the season on IR in each of the last two seasons so his release can't be considered a huge surprise. QB Matt Gutierrez was picked up as the emergency third quarterback last year and his release means QB Tyler Palko now holds that spot.
Banks, Jones and Landry were signed as undrafted free agents last month and realistically didn't have much of a chance to make the roster. Porter is a former wrestler that spent part of 2009 on the practice squad and was considered a developmental player.
This puts the Chiefs at 80 players (not counting Jarrad Page). They are allowed to have 80 players under contract right now. Remember, they haven't signed anyone from their draft class so this means that rookie signings are on their way.
Look for rookie signings to start filtering in shortly.