The important things to remember when explaining the technological differences between the two worlds is not that Walternate couldn't build a doorway like the original one Walter used to cross over. It's that he didn't because to do so would potentially destroy his world.
To begin with he only learnt where Peter had gone when Olivia crossed over and spoke to him thinking it was Walter.
Walternate didn't have William encouraging him to cross certain lines originally. Taking science in particular directions.
But then after Walter regretted his choices and had William cut parts of his brain out. (If we are to believe it was actually his choice.) William crossed over many times, in ways that I don't believe were made clear and began working on Walternate with the guise of supposedly keeping tabs on him. But all the while helping to advance technology in many new directions.
Some but not all the differences hang on that partnership and those ideologies that both bring them together and that separate them.