Neither Sunderland or wigan were in any way big games, as would have been entirely clear if we'd won them. It's sad that our fanbase are so short of glory that they try and project bigness onto a quarterfinal and a routine league fixture.
We needed to beat sunderland to keep up with the chase, yes, but no more then we needed to beat qpr, stoke, newcastle, sswansea, villa, sunderland, reading, southampton and all the other clubs we did beat and no more then we needed to beat norwich, southampton, swansea, fulham, newcastle and all the teams we didn't beat. We're out of the race for europe because over a season we haven't won enough games. Every game is a big game or, more sensibly, no game is.
Same with wigan. It was a cup game we needed to win but no bigger than bolton or oldham which we did win.
If in the last of week of the season we'd faced up to chelsea with a chance to get CL football and man city in a final, those would be big games and we could sit back and judge our team and how we did in big games to hearts content. (I would guess given our record in derbies and our performance in the one actual big game of Moye's time here that we'd be awful in big games, btw.)
But right now whether or not we're big game bottlers is entirely hypothetical because we don't win enough small games (like sunderland and wigan) to allow us to find out.