It is true that some of the APIs for our modular instruments use components from the DAQ driver to talk to the hardware. This is primarily for efficiency of development; for certain tasks, the low-level programming of one of our DAQ boards and one of our oscilloscope boards is very similar.
At the API level, the DAQ API presents a general purpose API that cuts across a lot of different kinds of hardware with a lot of different capabilities. We could extend the API to also cover all oscilloscope functionality, and all Function Generator functionality, and all High-Speed Digital functionality, and all Digital Multimeter functionality, etc. But doing so could make programming any of our hardware more difficult, because you have to understand
a lot more that may not apply to you.
So, we present different APIs for the different groups of hardware, so that each API can focus on making its own hardware powerful and easy to use.
For example, NI-SCOPE includes several measurements that you traditionally find on oscilloscopes, such as rise time, overshoot, etc. The NI-DAQmx API doesn't do measurements like this directly; you have to use Advanced Analysis functions to compute them.
I hope this helps.
Brian