what's missing in the American version?

What American version? I can't find head nor tail of it.

In the US version, Lucy and Sam have a prolonged separation. In a voice over Lucy says she didn't want to see him again but could never bring herself to divorce Sam. After some time passes (indicated by the length of his hair and beard) Sam tries to see Lucy but she turns him away. He is persistent and tells her that he will be in the park every day waiting for her. After a period of time Lucy sees the film he was making and realizes it was actually a love letter to her (and Dick and Debbie). She goes to the park to see him and they reconcile.

In the other ending, which you can see on You Tube, Lucy has an affair with Carl Phipps and finally becomes pregnant. Although Carl says many of the right things, he also says he thought Lucy was infertile and was not expecting that she would be able to conceive a child. It's obviously not an ideal situation for anyone involved. Lucy is Carl's date for the premiere of Sam's movie. They make a stunning couple in their formal wear, but Lucy notices he preens too much in front of the mirror, and he virtually abandons her at the premiere so he can give interviews (politicking for the Bond role). She sees Sam at the theater but rebuffs him; she goes home alone. Lucy goes to the park where Sam told her he would wait for her and they talk. She has lost the baby and is no longer seeing Carl Phipps. Sam and Lucy reconcile. The fact that she was able to conceive with Carl apparently gives Lucy and Sam hope that they may yet become parents, there follows a montage of their intimate moments in wildly inconvenient or inappropriate times and places.

It was kind of disappointing that Carl Phipps, who had been built up throughout the entire movie as the epitome of romance, excitement and genuine caring sympathy for Lucy, turned out to be such an ass at the end.