You might say that a flight to Singapore only takes 45 minutes. But then you have not factored in the time to get to the airport, check in and wait at the gate before departure, and also when you reach Singapore, the time spent on claiming your luggage and so on.
A memorandum of understanding was signed in July between the Malaysian and the Singaporean governments for a 350km high-speed rail (HSR) link between KL and Singapore (Jurong East). Such a link would be most welcomed by people on both sides of the Causeway. If all goes as planned, it is expected to be operational in a decade.