During the recent years (5 or so) we have seen the rise of many relatively small and simple applications each of which is responsible for either one or a few tasks. One of the most notable examples are the applications by 37signals: each of their apps takes care of just one aspect of the business and does it well.
What I am concerned about is the fact that small businesses (the target market of 37signals and other such companies) must subscribe to at least 3 or 4 different apps (perhaps from different vendors) to meet their otherwise uncomplicated requirements.
This may amount to a quite high monthly fee if all subscriptions are added together. Sure, the makers of such applications don't really see this ($20 a month per client is not much) but for the small business is a small fortune when added up (~$150). Despite this, it seems to me that this way of doing business (sell many different apps to the same company) is working well.
My guess at the moment is that it depends on the application and whether the target business can afford to not use it.
As an added benefit, thanks to the fact that most of these services use monthly billing it's possible to stop using the service when you need to or at least allowing you to downgrade a to a version that meets your requirements, helping reduce monthly burn.
The only downside is that integration between various services often involves bubble gum and duct tape. Or maybe that's an opportunity for entrepreneurs. :-)