What's your take is eShop low or high risk if you are going to launch a title that has the same quality level and budget as a full retail? Assuming you are a developer capable of getting your game to retail in the first place. What is riskier?
If your title is a full-budget game, going digital-only is a stupid idea. As many have pointed out, the digital market on handhelds/consoles is much smaller than the retail markets for those same devices. Even large-scale public exposure does not seem to completely counteract this; Shadow Complex on the 360 received a large marketing push from Microsoft, including a fairly prominent spot in Microsoft's E3 conference, yet I recall its developer stating that its final profit was relatively minor.
To answer your question more broadly though, going digital is a smaller risk, because it lets you skip much of the high costs of publishing. While the distributor's cut seems to be comparable to what the retailer will take, a digital game does not have to take the risk up front of paying the platform holder upfront for the discs etc., or a logistics company to get those copies to retail. If the digital game bombs, sucks to be you. If the retail game bombs, sucks to be you, and here's the bill.
And for what its worth, the 3DS market is growing. Dillon's Rolling Western sold somewhere around 25,000 copies its first month. Given the growth of the 3DS, it's about assured to eventually hit 100,000 or more due to its great review scores from users. With the publisher getting a 70% cut of revenues, that is a nice chunk of change for them.
I'd imagine the publisher in this case is taking more than just 70%.