Continuity mistake: When Bridget is getting dressed for her big date with Daniel, her tights are over her undies; later, when he's going up her skirt, the tights are clearly under her big ugly undies. (00:17:50 - 00:26:00)
Continuity mistake: After Mark Darcy and Daniel Cleaver fight in the street and Bridget goes to comfort Cleaver, Mark Darcy flings his jacket over his shoulder as he walks off. You can see very clearly that the white lining of the sleeve, flapping around as he walks. When the camera cuts to his receding back, the jacket is perfectly flat and smooth down his back, and the lining is no where to be seen. (01:12:20)
Continuity mistake: Tom is changing the fascia of his mobile phone. When we first see him, he is holding the phone up to his shirt and the fascia is blue, he then puts the phone down near to Bridget. It then cuts back to Tom and the phone has moved nearer to Jude and the fascia is green. Tom then opens the box in front of him and hold the blue fascia up so it falls out of the plastic wrapping completely, just before a man comes up to ask him if 'he's the bloke who sang that song' he is getting the blue fascia out of the plastic wrapping again. (00:10:50)
Revealing mistake: When they're driving back to the Darcys' in the snow, you can see that as they pass through the village near the house, the snow on the ground is in fact a white ground sheet and has not been pulled up to the edges of the wall surrounding the green. (01:17:25)
Continuity mistake: Towards the end when Mark Darcy finds her diary, you clearly see the number 29 as he pulls it from under the magazines, then when you see the diary it's open on pages 10 and 11.
Continuity mistake: After Bridget sprays the contents of the blender all over herself, there's a splodge on her right cheek - it changes shape when she answers the door. (01:01:10 - 01:02:00)
Continuity mistake: While Bridget and Daniel are driving to their "full-blown mini-break holiday weekend", Bridget lifts the sunglasses over her forehead with her left hand and holds the scarf at her neck with her right hand, but in the next shot before her scarf blows off her hands are in the opposite positions. (00:31:10)
Answer: Lots of times in book-to-movie situations and even in some remakes, the producers/writers/directors change names or events. It can be because of personal issues, legal ones or it can even be spur of the moment. it can also be unintentional,when they change it without the specific INTENTION to change it. I think in this case it was more likely that the character/or their name didn't have too much of an impact on the story line, so they didn't feel a pressing need to keep it the same.