Translation:The chairman is elected by the members.
They do mean the same thing, but they serve different grammatical functions.
väljs is the passive present tense of välja, turning jag väljer dig into du väljs av mig.
väljas is the passive infinitive of the same word, which means that it functions in the same way other verbs do in the infinitive - that is, mainly with modal verbs. For instance: du kan väljas av mig = "you can be chosen by me".
The s-passive denotes action and the perifrastic denotes state. So with habits being actions, you use s-passive for those as well.
- OS hålls vart fjärde år = The Olympic Games are held every fourth year
- Sången spelas minst en gång om dagen = The song is played at least once a day
- Medicinen ska tas klockan tre = The medicine is to be taken at three o'clock
As you can see, the line between once and habitual can be blurry. The medicine example, for instance, could very well feasibly mean either.