The first season was filmed entirely on location in London (UK) for Los Angeles. In fact, Matt LeBlanc's beachfront 'Malibu' house is located in North London's Mill Hill district. Camden Town (London) doubles for Las Vegas. A Pinewood Studio car park was used to replicate a Burbank Airport scene.
One of the main, if not the main reason why there's generally a year and a half gap between seasons is because the creators made a deal with Showtime and BBC in which they are allowed to write the whole seasons before shooting begins.
Matt LeBlanc revealed in an interview that, because the whole season is written in advance, scenes from different episodes are shot in a row, based on the location available.
Claire Forlani and Thomas Haden Church were on the original pilot of the show, but when the series went to production, they dropped out. Forlani was replaced by Tamsin Greig and Church's role was scrapped.