>> Is there any reason (apart from oversight) for that ? Does it matter ?
> Interesting. I have no idea.

I doubt that it matters. In this instance bultin::stringify is doing the same thing to its argument as interpolation does:

D:\>perl -MDevel::Peek -le "$x = 100; $y = \"$x\"; Dump $x;"
SV = PVIV(0x1d14cb52750) at 0x1d14cb54110
  REFCNT = 1
  FLAGS = (IOK,pIOK,pPOK)
  IV = 100
  PV = 0x1d14cb85630 "100"\0
  CUR = 3
  LEN = 16

D:\>perl -MDevel::Peek -le "$x = 100.5; $y = \"$x\"; Dump $x;"
SV = PVNV(0x1ba09babdd8) at 0x1ba09be1070
  REFCNT = 1
  FLAGS = (NOK,pNOK)
  IV = 0
  NV = 100.5
  PV = 0x1ba09c47d00 "100.5"\0
  CUR = 5
  LEN = 48
[download]

If there was a problem with that, then it would likely have already been encountered.
(I actually have a vague and hazy recollection that this difference wrt the pPOK flag serves a purpose.)

Thanks also to jdporter and davido for their helpful inputs.

Cheers,
Rob