Indeed, Walsall are not happy at all that their game v Leicester was overlooked for main live BBC/ITV showing, although it is on the BBC red button coverage. The very similar looking Gillingham v Leicester match was chosen from a pool of 32 games in round 3 and Man Utd v Reading has zero interest for any neutral yet has been picked ahead of it in round 4.
Walsall do get Gavin Ward for his first game there for almost 7 years, so every cloud and all that ! 
I think it's very likely a Manchester United game would rate higher than Walsall v Leicester, which is always going to be a prime consideration for ITV as a commercial broadcaster. If the FA want the TV companies to bid for the rights and give the cup some prominence then they'll need to have some acceptance that teams like Manchester United and Liverpool are likely to be regularly shown.
The BBC had Preston V Spurs, Accrington Stanley V Leeds and the exciting Wrexham V Sheffield United on BBC1, so the traditional cup tie element was certainly well covered. And of course we're getting more live games from the FA Cup than ever before really, with comprehensive Free To Air coverage. 15 years ago you'd have had 3 live games on BBC1 and 1 on Sky and that would be it, whereas now there's 3 on BBC1, 4 across ITV and a bonus one on the BBC red button.