HTC is in a tough place because samsung manufactures its own devices. Is one of the biggest manufacturers of most of the components in a smartphone. So they bring out any and all the new tech to their main phones as soon as possible and make it very hard for others to compete as Samsung is 6 months ahead of the rest of the Android OEMs.
I think that's is one of the reasons even Google went with Samsung for its Nexus phones.
I don't think people have to worry about stagnation in Android even if Samsung is the only one left standing as Samsung is competing with Apple so is still going to push the limits where ever possible. Android main growth now will come from India, Indonesia, China, Brazil where I don't think apple will grow much more as its devices are simply put to expensive for most of the people. Android went from almost nothing to over 50% in china.
I live in Singapore where 90% of the people used to use Iphone so much so that under many contracts Telcos were giving it for free to get users. About a year ago In a group of 10 people 9 used to have a smartphone and 7 or 8 would be iphone. Now its 4 samsungs 4 Iphone 1 some other brand. Most of the people using samsungs have a GS3 or Note which is huge hit among the older generation.