Funny what a difference a year makes in the perception of the domestic box office.Last year, when “How to Train Your Dragon” opened at $43.7 million, it was widely reported as a soft opening. This weekend’s champ “Rio” – which was tracking in line with “Dragon” but came up short at $40 million – is celebrated as a success for Fox and the sign of brighter days ahead. What gives? In a nutshell: These are different times. When “Dragon” bowed on March 26, domestic box office was chugging along at a record-setting pace, thanks to 3D pics “Avatar” and “Alice in Wonderland.” Both of those titles set the bar high for subsequent 3D releases, including “Dragon,” which many pundits thought would ride the 3D wave. It didn’t, at least not the way most anticipated. One major industry headline bluntly stated: ” ‘How to Train Your Dragon’ starts modestly.” But when all was said and done, Par’s “Dragon” became one of 2010′s highest-grossing films, cuming almost $500 million worldwide. That film benefited from strong reviews and sturdy legs that helped carry it well beyond Easter and into summer months. With “Rio,” 2,591 3D locations (“Dragon” had 2,364) meant more opportunity for higher 3D ticket sales, though Fox’s toon earned 58% of its opening from 3D vs. 65% for 3D “Dragon.” Still, “Dragon” likely helped pave the way for “Rio,” particularly among family auds who normally wouldn’t be willing to pay for 3D premiums. Either way, 2011 was simply an easier playing field for “Rio” – at least when it comes to battling industry and media perception.