IGH with chain is nearly maintenance free. You barely have to oil/clean the chain....I rarely do....just ride it until the cog and ring are thrashed and then replace all 3. Without a derailleur the chain will keep going 'round happily for a very long time without much attention...especially if your cog and ring have even numbered teeth as Sheldon points out:
http://www.sheldonbrown.com/chain-life.html
With a Rohloff just flip the cog and ring and add new chain for a whole new lease on life with minimal cost - I run $16 SRAM 8 speed chains on my Rohloffs.
I have not experienced any difference in this regard between a decent derailler (like Tiagra) and my IGH bike. Both required adjustment after 100-300 miles for optimal shifting. Neither really "requires" constant cleaning of the chain, they seem to work fine without it, and I can just run them until the chain or cogs wear out, though I have no doubt there's a certain number of people who feel the chain should be cleaned regularly - I try to do it once a year, but in the past I've gone years without cleaning a chain on a derailler setup. A rear cassette seems to be slightly more expensive than a rear single ring. As I mentioned - there's not much of a difference for regular road riding.