Sub-System Interconnections - Wireless versus Cables
For sub-system interconnections, there is an increasing trend towards wireless connectivity (rather than cables) because:
Any 'active' electronic device offered for sale must comply with the EMC directives of the target country, eg in the UK and Europe, there are the EU directives, in the USA, there are the FCC regulations, etc.
Using wireless connectivity provides isolation between parts of a system that greatly reduces both noise emissions and susceptibility of the total system.
Cables impose a physical constraint on both distance and flexibility of movement. Also, due to the length of a cable, there is an inherent antenna effect.
Wireless connectivity allows infinitely flexible movement and more reliability due to fewer connectors. Also, there is reduction in both noise emissions and susceptibility due to the absence of the antenna effect of a cable(s).
Initially, cables may seen as the lower cost option but when the cost of EMC/compliance testing is taken into account, wireless connectivity may result in a lower total cost.
Infrared vs RF Wireless - WiFi, Bluetooth, ZigBee etc
To integrate Bluetooth into a product, you need:
A Bluetooth device has rich functionality, eg must handle multiple nodes etc. To support the required functionality, a complex stack is needed which is much larger and complex than a IrDA lite stack. A pure software implementation of Bluetooth, while possible, should be bought-in and consumes substantial CPU resources. Generally, a proprietary chipset is the usual option. Both of these options dramatically add to the unit cost, typically, more than 10 USD per unit.
Because a Bluetooth product is inherently an RF device, expensive RF related EMC/compliance testing is required.
The same issues apply to any RF wireless technology - WiFi, ZigBee etc.