The precise software and version numbers of what you are running is no ones business but yours. If an attacker knows exactly what you are running, they know what exploits will work, and which ones will not. It saves them a lot of time. A lot of worms and automated cracking tools look for this information, too, as part of their modus operandi.
Some software can be configured to hide this information, others may need to be recompiled, but one way or another it's a good idea to conceal this information.