Something some one said today actual kind of clicked with me and i think its kind of relevant to this discussion. Mind you it was not expressly about soloing, but it was more geared towards Difficulty.

I am paraphrasing greatly here so stick with me.

"Ya know, I don't really have a problem with a game developer adding in a easy mode for people who cant deal with normal or harder difficulty setting. In fact i think its a good thing, It helps them learn the ropes and to become better players. there is also the benefit of every body no mater the skill level getting to see the content. The problem i have is when they take content and make it exceedingly easy for every one for the sake of players who are not able to hack the normal setting"

he later went on to say that rewards for said easy mode certainly should not be as large as normal or hard. But there's nothing wrong with a the game giving a easy mode player a pat on the head and a shove of encouragement to rise to the challenge of the harder difficulty settings.