I'm bootstrapping my current startup, and putting up a splash page would have taken me a couple of hours to set up a slicehost server, install a simple php script, or web framework du jour, and then code and design the splash page with the "put your email in here" form.

At this point, on my day job, my time is worth $75 an hour. So, if I can save 6 minutes, I've saved myself $7.50. By spending $5 a month on launchsplash, I've saved myself about $250 worth of my time.

It's not a matter of having to use the service. It's a matter of expediency. The quickest/cheapest way to get from point a to point b for me is to outsource my splash page and email collection right now. It's not a core competency, why not outsource it?