I definitely hear your point about the timing and wording of the reboot message. I'll look into ways we might be able to improve it, but unfortunately, all of the issues you ran into during install, including that message and the reboot itself, come not from SketchUp, but from the installer for the .NET Framework 4.0, which is provided by Microsoft.
The .NET Framework is the only non-standard element SketchUp requires of your Windows machine. Most users already have it, but in case they don't, the first step we take is to invoke a bootstrapper program, which contains a provision to download and install .NET Framework from Microsoft, before the SketchUp installer even runs. In most cases, that installer will be unable to complete its work while the system is running, and will schedule some remaining tasks to be done at reboot. That's the situation you encountered.
If we could, we would improve the messaging for this and defer the reboot to the end of the install process, but our only choices are either to let the reboot occur when the installer requests it, or to suppress the reboot from happening at all, as our installer cannot detect that a a reboot must still be done. Since it's rare that the .NET Framework needs to be installed, and even more rare that a reboot is required, we certainly don't want to force everyone to reboot after installing SketchUp, either.
In much older versions of SketchUp, we simply suppressed the .NET Framework's reboot function to avoid interrupting the installation flow. However, in cases where the reboot was required but not done, SketchUp would fail to launch, which is even worse than the reboot and ugly messaging. That's why for 2014, we decided the best compromise was to allow the .NET Framework installer to reboot the machine if necessary, and to gracefully resume the SketchUp installation upon logging back in.
I'm really glad we were able to solve your installation problem. Happy Sketching!
SketchUp Release Engineer