Ron,
The module vendors certify their product for FCC, ETSI and Bluetooth. While it is true that you will not need to do Bluetooth certification if you adhere to the TI reference design, you will still need to do FCC and ETSI certification.
Another advantage of the module over the discrete solution is a RF ready module, reducing the characterization and testing part. This is useful for folks who don't have enough RF expertise, need to get there product to the market asap or simply want a ready solution. Also, the module solution is usually a lot more compact than the discrete component solution.
The discrete component solution along with being cheap allows you tuning flexibility to overcome issues in the board layout. In the case of the module, you already have a pre-made/tested solution