NodeJS native Mongodb server sockets options for server and for replica - what's difference?

Replica set has socket options: http://mongodb.github.io/node-mongodb-native/2.1/api/ReplSet.html

Also, server has socket options http://mongodb.github.io/node-mongodb-native/2.1/api/Server.html

Now, I connect to my replica as

    var MongoClient = require('mongodb').MongoClient;
    var ReplSet = require('mongodb').ReplSet;
    var Server = require('mongodb').Server;
    var servers = [
      new Server('srv1', 27017, {socketOptions: {socketTimeoutMS: 100000}}, new Server('srv2', 27017, {socketOptions: {socketTimeoutMS: 100000} }, new Server('srv3', 27017, { socketOptions: {socketTimeoutMS: 100000}},]; 
    var replSet = new ReplSet(servers, {
socketOptions: { socketTimeoutMS: 666666 }
});

    var dbConnStr = "mongodb://user:pass@srv1,srv2,srv3/mydb?replicaSet=lw&readPreference=secondary";

    MongClient.connect(dConnStr, {replSet: replSet}, {function(err, dbConn) {
    //
    });

Now the question: what socket timeout is actually applied when settings for replica set are different from settings for each server in server array.

Also, bonus question: why do i need to set replica servers on connection string if there is an array in replica set object?