That's something that is striking; remember, back in ch270, Ichigo was told by Ulquiorra that Rukia was dead and he was an obstacle between him and Rukia. And now, Ulquiorra is not letting him protecting Inoue (ahem.. not sure about how Inoue would have been after his attack fired at her -___-"). So, the two situations can be compared quite easily ^^ And I'm adding a comparison with Nel's case with Nnoi to further my point :p [click on thumbnails to enlarge]
I think those pages speak for themselves XD
I put Ichigo's reaction for the kicks, because it does further my point. I think it's very clear that in both ch290 and 342, Ichigo shows anger; Ichigo is hotheaded, so he's someone who will get often angry for his friends' sake, it's not really a first for him. As NeoSapien noticed, the face he makes displays the same feelings: anger that someone threatens a friend dear to him.
However, it was different in ch270. I think it's one of the distinctive traits for IchiRuki; Ichigo never reacts the same way to Rukia as he reacts for other people around him. What Ichigo displays in ch270 is fear. For Ichigo, who's always cocky, hotheaded, who is often angry at his adversaries, fear is such a powerful feeling. And, since it's not often, it's always displaying a new light on his perspective. Here, in the first pages, Ichigo is crushed - he first doesn't want to believe that she's dead and the second after, he doesn't care anymore, he just needs to go by her side and save her all over again. Then, Ulq mentions Inoue, and he understands that Ulq will not let him go without fighting. However, he's in a hurry - of course, since Rukia's state is at stake. So, what does he do? He uses his mask - right away. He doesn't take a lot of time to think - it's more a oh this guy won't let me go to Rukia, I'm using full power to get rid of him
Whereas, in ch342 - I'm not comparing with ch290, because Ichigo was too tired back then - Ichigo still refuses to use his mask. Beside that, don't you think Ulq's words are very interesting? He doesn't point out that Ichigo wants to save Inoue, he states out that Ichigo wants to fight someone else. In ch270, Ulq never questioned his need to go back to Rukia and to save her - he told him it was useless, he tried to anger him with something else so that he'd fight and he managed to, but I think his reaction to Rukia's fall did startle him. Ulq obviously didn't think that Ichigo wouldn't let pass the chance to not fight, yet, for Rukia, here is Ichigo letting go of everything.
Also, for the lulz, since I wanted to do that a long time ago:
Does anyone else notice the difference between the two scenes? They represent exactly the same things though: Ichigo meeting up with the girl he needs to save for the second time... yet...