<h2>Why not use a dedicated server for each concern?</h2>
<p>You can! No-one's going to stop you, but unless each concern <em>requires</em> (i.e. needs the dedicated hardware/isolation) its own dedicated server, it's hugely redundant. Again NAS as an example, would be good for a dedicated machine, as it'll be safer if there's no additional chance it goes down due to failure of an unrelated service.</p>
<p>Virtual Machines are wonderful, as they allow you to make use of more powerful/high spec machines while minimising the wasted usage...</p>