I won't be able to post things next week, so here's some recycled material for approaching visitors. While searching through old email, I found the following post I'd made to the Gurpsnet mailing list.

In a thread on armored GURPS 3e fighters having much-too-high defenses, I respond to one poster below. 4e greatly alleviates the problem by eliminating PD, but it may still be an issue for some players. It does summarize what is to me an important point: the game should accommodate "too high" defenses when those are warranted! 

Imagine, if you will, a warrior with Plate Armour (PD 4) with Deflect +3, a skill of 22 with a broadsword, and Combat Reflexes. His total defense? A parry of 19. Now, the rules as written state that Sir Unhittable will be struck only if he rolls a 17 or 18 on his parry. Mathematically, that's a 1.5% chance of being struck.

1) I have implemented some of TBone's suggestions, such as causing Shields to inflict a penalty on enemy attacks rather than give PD, allowing fast blows and such. I have not gone so far as to eliminate PD on armour, however.

Doing this would certainly help... But sticking with other ideas for now:

2) I have ruled that a 15 or higher roll on a defense is always a miss. This is considered after all penalties, so Sir Unhittable above, facing off with an ork that uses a flail, has a modified parry of 15, and still only misses on a 15 or higher.

That's one way, but I wouldn't go for it myself. As others have already commented, is the incredible defense score here really bad? A good game system SHOULD allow for some cinematic combination of amazing skill and defensive aids that make a defender nigh-untouchable -- and it looks like you've found one such combination for GURPS. : )

The guy is the best swordsman in the land, wearing the best armor money can buy (with powerful magic enhancements to boot! Magic, mind you!!), and has a good weapon in his hand. Now stand him – rested and ready – before a line of nondescript challengers, and have them come at him one by one. He should knock aside each scrub's blow, and the kingdom should be awash with tales of the knight that can't be hit. That kind of character should be possible, and you've shown that it is. This is good.

But a merely impressive (not incredible) knight will have a more modest skill (17?), and no magic plate. He'll get hit more often. That's more the kind of knight you'd typically find as a PC or a foe.

More importantly, place either knight on a chaotic battlefield, and all bets are off. Even if few foes can Feint against Broadsword-22 or even Broadsword-17, all it takes is for two foes to attack at once (or one foe to use AOA and two attacks), and that amazing Parry is gone vs the second attack. And at any time, the lowest scrub foot soldier could easily stick a spear in this knight from behind. And so on.

That's my take. At the same time, twisting the topic a bit, I know many players have complained that even with more modest characters, defense rolls can be very high in GURPS, and combats long. Whether that's realistic or not is secondary; the point is that the combats are long enough to make these players complain! For these cases, I've found various ideas, as you reference, to be a help. Other players have suggested others. With these tweaks, I don't find high defenses to be the bugbear in GURPS that some players claim; they can be made manageable for typical fighters, or made amazing for amazing fighters. This is good, IMO!