Its absolutely fine and your choice.
But what baffles me is that how any program could only ask for a specific lower version. Generally we run across " Windows XP or higher, IE 5 or higher" and so on.
In this connection and related to .net, before ordering Nero 10 Multimedia suite, I made a quick research.
.Net 3.5 SP1 is one of the minimum requirements. The package itself will download it and install, if one does not have it already.
But then many people experienced problems with it during the installation of Nero 10 Suite.
In the light of this, I decided to download and install 3.5 SP1 independently before installing Nero 10 Suite. In the process I stumbled upon .net4, downloaded and installed it.
Afterwards installation of Nero 10 went on smoothly without any problem whatsoever. I then left a blog in the cnet forum that any one wanting to install Nero 10 suite may do well if they download .net4 and install it beforehand, to avoid any problems.
Nero 10 did not demand that it should only be .net3.5 SP1 and not .net4.