Well, I'm not sure what you mean by "lewd"- do you consider any song relating to sex as "lewd"? most of the songs on In Rainbows are about love or sex as a subject, to some extent, especially compared to their 1997-2003 work, which rarely was about that subject. When talking about post-EMI Radiohead, love and sex (and problems related to it- I'm not saying these are party songs) is actually the main subject of their recent work, like with most popular music, which marks a maturation in their art, that they are no longer afraid of dealing with that subject. You can say that maybe they are using this subject as a metaphor (for example, as a way to critique technology and capitalism and make environmentalist statements) but they are still writing about this. Sex and love are huge subjects in every religious text too, including very conservative ones. Religion, like art, is often a response to those areas of life and trying to formulate rules to control people's sex drive (and the social destabilization it may cause) or make sense of it in some way. Radiohead are no different- they need to write about these subjects because this is what people are doing or thinking about doing in real life. Sex will not stop existing if they ignore it! They will merely make their art feel dry and irrelevant to people's lives (including their own) if they avoid love or sex as a subject.

The fact conservatives in India will go to the trouble to ban even the word "nude" shows that sex is a very important obsession of conservatives in India too. They see that normal descriptive word and their minds get "dirty." And the subject of sex was what Radiohead was at least partly thinking about when writing Nude- but that doesn't say anything about Nude's actual attitude toward sex. Religious conservatives might actually agree with the song's attitude, which seems rather critical of sex. In fact, In Rainbows as a whole is about sexual fantasies (or using these as a metaphor for other types of fantasies, i.e. capitalist economy) but it is about that subject only in order to critique it. There is nothing particularly judgmental about In Rainbows like a religious text might have, but it shares the suspicion of sexuality you would find in many religious texts. The basis of the album's narrative is the Faust story where someone sells their soul for sex basically. And that's not seen as a good thing! Nor does Thom envision it as a good thing. But in order to show the "evil" of sex (if you adhere to that view) you need to show (as most religious texts themselves do) the temptations of it as well. You can't just pretend sex doesn't exist. Conservatives don't even do that- they obsess over it.

The song Nude's title may or may not have any particular sexual connotation, but considering that the lyrics allude to sex in a sly way ("don't get any big ideas" is an idiom used to reject sexual advances, and "dirty minds" are usually considered as sex obsessed) and the original lyrics directly reference it ("she stands stark naked and she beckons you to bed"), the title Nude was clearly chosen to reference something sexual, among other things. As you correctly note, there is nothing inherently sexual about nudity, but part of what this song is about is related to sexual fantasies. That becomes even more clear in the context of the next two songs on the album, Weird Fishes and All I Need, which (like most of the latter half of the album, too) are obsessively romantic in nature. And the preceding songs Bodysnatchers and 15 Step also related to trying to get the attention of the object of one's desire (and failing) and then being conscious of one's physical body (and being under someone else's control- nonconsensually). Sex is very present as an undercurrent in In Rainbows.