I was thinking on the same lines... I was thinking more the fact that Charlie takes the place of Penny.. Desmond can't have both saving Charlie and being with Penny again..

In his flashes last night it had Charlie dying and Penny being the one in the tree...
In flashes before your eyes, when Des is figuring out that everything is happening again he takes off his tie and throws it on the ground.. Then he said Penny asked me why I did that.. But then he see's Charlie and there is no Penny there...

I guess I find it odd how when Charlie is involved Penny isn't...
That and at some point Charlie and Penny both lived in London.. I think Charlie grew up there and Penny's dad's corporation is also in London!

__________________
Please don't give up, Des. Because all we really need to survive is one person who truly loves us. And you have her. I will wait for
you. Always. I love you, Pen

DESMOND: I love you, Penny. I've always loved you. I'm so sorry. I love you!
PENNY: I love you too.
DESMOND: I don't know where I am, but--
PENNY: I'll find you, Des--
DESMOND: --I promise--
PENNY: --no matter what--
DESMOND: --I'll come back to you--
PENNY: --I won't give up--
BOTH: I promise. I love you.