It's less risky because you don't need to sell as many copies in order to see a return on your investment.
Even with an outside investor.
A game doesn't need to be a smash hit AAA title to make profit. Yes, you will get some developers/publishers that will only be interested in going for games that they think will sell the most, but it doesn't have to be that way.
EDIT:
BW, where did you hear you have to buy Garry's mod? Steam tells me it's third party, and when I go to his website, it has download links right there.
As for "the Ship," was it ever actually released as a mod (for Half-Life)? If so, what's to stop you from still playing the mod? Just like how I don't need to pay to play CS:S with my retail copy of Half-Life 2 (nor did I have have to pay to play the original CS, even after it went retail, with Half-Life).