I think it probably depends on your community on what is "normal" but I think, in general, kids learn to read in kindergarten. They are not expected to know before starting school.
I do NOT think that you need to be worried or concerned. It sounds like your daughter is normal to me, and that other children are more advanced. I do NOT think that means that she will always be behind, or that those kids will always be accelerated.
For your son, make sure that you read with him every day, talk about what you read, make predictions about what will happen next, make connections about the text to his life, and track the words with your finger. Also do lots of rhyming with him - songs and poems and try to get him to hear the rhyme and come up with other rhyming words.
Maybe get the first 100 sight words off the internet, and do games (memory, go fish, bingo, etc) with them with both of your children.
Its silly and weird that the teacher acted like it was your fault, or the preschools fault, that your child did not already know how to read at the beginning of kindergarten.