First a disclaimer:
I am a friend of Atul's and it is me who suggested him to become a reseller for NMT as I am a very happy user of popcornhour.
Comparisons:
HTPC vs NMT : You can never beat what a HTPC does with an NMT. But there is always a cost differential. I had built my own HTPC using Linux before I bought the NMT and even setup Myth TV. But a good HTPC costs more. Also, more importantly for me, the power consumption of a HTPC is much more than an NMT and I generally keep my NMT on always to download youtube videos etc.When the Atom based HTPCs hit the market, then I guess the NMTs will take a back seat, but who knows, I hope then the NMTs will also reduce the cost to maybe below $100

. We can certainly wait till the competition heats up, but if we want an NMT now then the price is as specified by popcorn hour and others.The best way to get an NMT now maybe is to ask a friend coming from US to get one so that it will cost only $215 or ~Rs.10750. But even he has to pay shipping as popcorn hour is not available in stores, so another ~Rs.1000-Rs.1500 and legally he has to pay customs that is around Rs.2500. So even for a guy getting an NMT from US will end up spending around Rs.14000.
WD TV vs NMT: Both are based on the same sigma processor, but for me the clincher was network connectivity and Media service portal. I can watch comics, Apple trailers, youtube, Flickr and Picasa photos online directly from my NMT which I cannot do with an NMT. Additionally it can download bit torrents. Though I would advise to download only legal bit torrents, like the Elephant dream HD etc. In any case, there are a lot of comparisons between WD TV and NMT on the web and a google of WDTV vs Popcorn hour will show very good results.
In any case, the service of popcorn hour is also really great. My second popcorn hour had a small issue with the optical output, all I had to do was send an image of the drive over email and I got a replacement in a week.
Personally, I think HTPCs are better for us geeks

, where we like to tinker around and even if it costs a little bit more, it is much more satisfying. (Though popcorn is also very geeky, you should see the changes I have made to mine

). But if you want to get something, plug it in to TV and directly watch some movies, i think the pocorn is better. But this is just my personal opinion.
p.s: I saw one reply where someone had built a HTPC for around Rs.12000. It would be really great if he can maybe gives us the specs so that we can also build one similarly.