flush-to-zero behavior in floating-point arithmetic

Yes to both questions. There are platforms that support flush-to-zero only, and there are many platforms where flush-to-zero is the default.

You should also be aware that many embedded and dsp platforms use a "Denormals Are Zero" mode, which is another wrinkle in the floating-point semantics.

Edit further explanation of FTZ vs. DAZ:

In FTZ, when an operation would produce a denormal result under the usual arithmetic, a zero is returned instead. Note that some implementations always flush to positive zero, whereas others may flush to either positive or negative zero. It's probably best not to depend on either behavior.

In DAZ, when an input to an operation is a denormal, a zero is substituted in its place. Again, there's no general guarantee about which zero will be substituted.

Some implementations that support these modes allow them to be set independently (and some support only one of the two), so it may be necessary for you to be able model either mode independently as well as together.

Note also that some implementations combine these two modes into "Flush to Zero". The ARM VFP "flush to zero" mode is both FTZ and DAZ, for example.

ARM Cortex cores have a flush to zero option, hard to see how you can ignore it. Then again, don't take business advice from a forum. Talk to your customers.