Quoting: Ste_Catherine_Street
The difference is Colorado already has stellar defence. Buffalo isn't close to contending. Edmonton is missing stronger dmen to contend.
Every team is different man, cannot compare apples and oranges.
You're out to lunch. Nobody trades good young players who are on their ELC's - especially a team who is stretching the cap as far as they can in order to contend. Besides, Bouchard and Broberg don't play the same position and their skillsets are quite different. There's no either/or situation here at all, to suggest that there is is just completely illogical.
They have Nurse-Ceci hard matched against the opponents best, and Kulak and Barrie to compliment Bouchard and Broberg. They aren't hurting for veterans on the blueline.
Let's look at the experience factor for Edmonton in comparison with Colorado:
Nurse: 477 GP
Ceci: 627
Kulak: 334
Bouchard: 102
Broberg: 23
Barrie: 683
Total: 2246 GP
Toews: 235 GP
Makar: 178
Girard: 340
Manson: 475
Byram: 49
Johnson: 857
Total: 2134 GP
So Edmonton's defense is actually the more experienced of the two teams. Their top-4 is significantly more experienced too, at 1540 games vs Colorado's 1228.
I don't know exactly what you're referring to when you say "stronger", but we can easily look at physical dimensions too:
Nurse: 6'4, 221 lbs
Ceci: 6'2, 210
Kulak: 6'2, 197
Bouchard: 6'3, 194
Broberg: 6'3, 200
Barrie: 5'11, 197
Average: 6'2.2", 203 lbs
Toews: 6'1, 191
Makar: 5'11, 187
Girard: 5'10, 170
Manson: 6'3, 218
Byram: 6'0, 195
Johnson: 6'4, 225
Average: 6'.08", 197 lbs
So Edmonton's defense corps is bigger and heavier, and their top-4 significantly so: 6'3, 206 for EDM vs 6'0, 191 for COL.