Skyjob, have you actually flown the 737, or just read the manuals? VNAV is a bag of nails which has a terrible tendency to overspeed, especially as it first enters descent at high levels with a higher cost index, and will still finish its arrival on height but way fast, making the approach unstable unless you intervene earlier.
The best way of avoiding it is to cheat the FMC descent winds with an extra 30kts tailwind or hit "descend now" or "alt intervent" 10 miles before TOD. Even then, VNAV can occasionally be glitchy, refusing to descend at all or levelling off despite the FMC and MCP settings being lower. When it doesn't do what you want, just over-ride it with LVL CHG or V/S. Use VNAV, but don't trust it.