Size and physical play are nice to have, but ultimately they are accessories and not necessities when building a Cup winner. When building a Cup-winning team, there are three required ingredients:
1. Center depth/skill (offensively and defensively)
2. Defensive depth/skill (offensively and defensively)
3. Good/great goaltending
If you have all three of those ingredients, you can surround them with skill, grit, whatever you feel increases your chances the most.
If you are missing an ingredient, you need to find a way to either fill the hole, or compensate for it. For example, in 2010 Chicago won with Patrick Sharp at center on the second line. This year Sharp has been on LW, and guys like Handzus and Kruger have been centering the second line. But even with Sharp on the wing, they make up for the gap. Because they have strong scoring in Kane, Hossa, Sharp, Bickell, and Saad, as well as the other wingers. Plus guys like Handzus, Sharp and Hossa bring a solid defensive game as well.
In 1986 and 1993, Montreal won the Cup without good offensive depth at center. This was countered by strong defensive play and an elite goaltender. New Jersey pulled off the same trick in 1995. Carolina was missing the defense aspect in 2006, but was very strong in terms of defensive forwards and their goaltender had an excellent (and Conn Smythe winning) run. Those four teams are the only ones since 1980 to win the Cup without possessing all three aspects I listed above.