Yes, comparatively speaking (hardware wise), Vista can be faster at launching programs. This is because of "Superfetch". In Windows Vista, Superfetch automatically loads programs into RAM on boot-up based on program use history. So, any program frequently used will load faster.
I own a MacBook Pro and have always noticed that first launch of any program in OS X is slow. Fundamentally, OS X and Windows are very different in terms of RAM utilization.
In 10.5, any icon with a blue dot underneath it in the dock, signifies that it's program is loaded in RAM and ready to go. Quitting (not closing a window) a program will then unload it from RAM. So starting Safari for the first time in a session will take longer than opening a new Safari window (after the program has been loaded). In addition, quitting Safari, then re-launching it will require OS X to reload it into RAM which in return will cause a slow launch.
Windows is very different; as it automatically manages your RAM. "Superfetch" aside, Windows too can be slow when launching programs for the first time in a session. The big difference is, there is no "quit" option in Windows; only "close". So, you open Internet Explorer for the first time and it takes a couple seconds, and then you close it. Then, for the remainder of your session, assuming you have sufficient RAM, Internet Explore will open quick every time you start it. With the addition of "Superfetch" and a fast computer, your most frequently used programs should always open fast.