One of the more enjoyable things about the FA Cup is that, if enough big Premier League clubs get matched against one another you can mentally begin to line up the dominoes and hope they fall. The 3rd round was a good example of that scenario; four Premier League teams (including last years winners Manchester City) were bounced from the competition. At least six others-including one of Liverpool or Manchester United- will be eliminated in the 4th round, meaning a maximum of 9 of the final 16 teams will be from the top flight. It's just so much fun to envision two or more of the remaining big sides being drawn against each other in the 5th round and paving the way for a Watford-Swindon (or something) final, despite the fact that A) it won't happen and B) that game would be awwwful, because the unknown weirdness factor is enough to make the downsides easy to look past.
Now, that's not to say the latter rounds could be a bit more interesting than they may have been in recent years. Liverpool and United are both clubs that could easily be envisioned as winners, so for one of the two not to make the 5th round would certainly open things up a bit. Arsenal appear very vulnerable at the moment, and though Aston Villa isn't the world's most threatening side it would hardly be a shock to see the Gunners bounced early. Any Premier League side is talented enough that a deep run in the tournament is well within reach (remember Portsmouth?) so to have them knocking each other out of the going in the early stages makes an unlikely run from a minnow far more of a possibility.
But for all of the big-club attrition, Spurs are still playing Watford and Newcastle are still taking on Brighton. The odds are very good that four of the top six teams in the Premier League will still be around after the weekend, and the odds that all four will be matched up against one another in the 5th round are quite poor. The very thing that makes the FA Cup so much fun in the earlier rounds is the thing that makes it kind of annoying in the middle and later rounds; sure, there could be giant killings and an inspiring run by a lower-league team. It's even plausible enough to play out the scenarios in your head. But sooner than later, those scenarios are going to get blown to bits and if there is an unlikely run to the final it's going to be made by a Premier League club that no one likes. Swansea losing 1-0 to United in the final is really the best case scenario.
In other words, the FA Cup is nothing more than a reminder from those on high that, while it's fine to indulge in every now and again, hope is ultimately futile. Yes, the 4th round (and likely the 5th round as well) offer some glimmers of a more interesting and inspiring conclusion, but you'd better enjoy it while you can because it will be gone in a flash. But you can always trick yourself for a few days.