The most logical analogy I can think of is the mobile phone vs. the digital camera: you can take photos on a phone but would you use one for your wedding photos? A digital voice recorder, like a digital camera, does one thing and does it well. Buttons are logically positioned, the microphone sensitivity and recording quality is adjustable and recordings can be downloaded easily without the need for proprietary software.
The fantastic new iPod Nano now has a voice recorder function. Handy for the quick reminder but a bit limiting for lecture or meeting recording. Why?
The Nano has one recording quality setting: 44.1 kHz, a sampling rate usually reserved for recording music, which means an hour of recording is about 60MB – not ideal for emailing or transcription (typing-up).