I think you really have to look at the big picture here.
Yes, Brady is under contract for 4 more years, but contract years don't guarantee performance. I don't know why people are assuming that he'll play at a continued high level just because he's under contract (it kills me to type that), and the drop-off can come quite suddenly. Sure, John Elway went out on top, but he also retired early. For those who continued to play until they were forced out, the end came a lot quicker than anyone could have anticipated.
Dan Marino played until he was 38. When he was 37, he had a decent season by his standards, 57% completion, 23 TDs/15 INTs, 80.0 Rating. The next year, it dropped to 55%, 12 TDs, 17 INTs, 67.4 Rating, and he was done. At age 35, Jim Kelly went from 22 TDs/13 INTs to 14 TDs/19 INTs a year later. Brett Favre had arguably his most productive season at age 40 with 33 TDs/7 INTs, then perhaps his worst the next year with 11 TDs/19 INTs.
So yes, Brady is under contract for 4 more years. However, to assume he will be a starter-level QB is not guaranteed. For all we know, Jimmy could be starting next season.
Also, I think we all agree we need a replacement at some point. For those who think we can get one a year or two down the road, I'm just not convinced you can order a starting QB easily when you need one. Both Kiper and Mayock stated this year's draft had a lot more draftable QBs than usual, so it may well be that this was the best year to dip into the QB replacement pool. JG might be better than all of the other options we'd have in the next few years, so if you believe he's the guy, why not invest the pick?
Any team investing in any QB with a top pick will carry some risk, and if that prospect doesn't work out, it hurts that team, regardless of where or when they're drafted. Even desperate teams that can easily justify the risk get hit hard when a QB prospect doesn't work out (Vikings and Ponder, Jaguars and Blaine Gabbert). We've taken a risk, no doubt. But we've also done the best job to minimize that risk, by bringing him in to learn from Tom without being pressed into duty to replace a legend.
And the reverse is true as well; when a top QB prospect hits, it doesn't matter when or where they were drafted. Think Packers fans are still sad about the team "wasting" a 1st on Aaron Rodgers when they were starting Brett Favre?
The bottom line is quality starting QBs are not easy to find. For those who call it a luxury pick, I disagree. Just because the timing might not be as convenient as some would do in their Madden games doesn't mean we have the "luxury" of picking a great QB later on when we're ready.
