HTML5 is a browser based technology. No matter how robust they become, desktop applications won't disappear, which is why the second part is fallacy. Even Silverlight has its place in Microsoft's strategies. HTML5 is the language of choice in Microsoft for internet applications; Silverlight is still Microsoft's language of choice for intranet applications. There is a big difference.
Let's see someone do this
float *xr, *xi, r0, i0, r1, i1; // And if it didn't fail above, it will here.
float *cos_tw, *sin_tw, c, s;
int N4, N2, N34, N54, n;
N4 = (m_plan->N) >> 2;
N2 = 2 * N4;
N34 = 3 * N4;
N54 = 5 * N4;
cos_tw = m_plan->twiddle;
sin_tw = cos_tw + 1;
/* pre-twiddle */
xr = (float*) m_plan->fft_in; // Oh god... This will destroy...
xi = xr + 1;
for(n = 0; n < N2; n += 2) // Bring on the nukes!
r0 = mdct_line[n];
i0 = mdct_line[N2-1-n];
c = cos_tw[n];
s = sin_tw[n];
xr[n] = -2.f * (i0 * s + r0 * c); // KILL! MAIM! DESTROY!
xi[n] = -2.f * (i0 * c - r0 * s); // RUB IN SALT! POUR IN IODINE!
// etc. etc.
Different technologies have different places. Trying to force them into the wrong hole is doomed to failure.
It's the whole "I have a hammer, so everything looks like a nail" thing. Well, there are such things as screws out there as well...
That only means that some cool stuff will get added to Windows 8. It doesn't mean that everything else is invalidated.
Microsoft fully supports F#. For a reason. It does a job that other languages don't do.
While JSON looks like crippled XML, it does have a purpose, and fills a role that XML doesn't neatly fill. Can you be more expressive in XML? Sure. Is that always needed? No.
It kind of reminds me of kids complaining about not liking math. Well... It turns out that sometimes you need math... It also turns out that sometimes you need to know a bit about history, and sometimes about geography, and sometimes about chemistry, and sometimes about...
I only see the new goodies in Win8 being a good thing.