You can definitely write your business layer in ColdFusion, and as you say you can extend that with easy hooks to java and .net objects.
The business case for ColdFusion is that it is a rapid application development platform - the speed that you as a developer can get things done is just insane. There is a lot of built-in functionality, from MS Exchange integration, charting, Excel generation, all the way through to a Hibernate ORM implementation (new in CF9).
There are a few popular, mature MVC frameworks (Model-Glue, Coldbox, Fusebox, onTap, etc) that you can work with, or you can run up your own framework using a pattern that suits your style.
What might be confusing you is that you can choose to write the presentation layer and business layer in ColdFusion tags, and that might be why you think it's not a powerful option for the business layer. CF tags wrap a lot of functionality in an easy to use syntax, but with CF9 you have the option to write ColdFusion Components (CFCs) completely with a script based syntax - that might help you distinguish between presentation (tags) and business logic (script).
The developer edition is free to try, so you really only are losing some time if you give it a go, and I highly recommend you check it out.