In both cases are police deliberately over emphasising the threat by using these politically charged terms?
Strict legal definitions used in the criminal justice system are often different from common parlance or from military definitions.
The Boston bomber was charged with using a WMD because according to US criminal code, any explosive device is considered a WMD. Police aren't in the habit of just using random terms when they legally charge someone with a crime.
IED does not imply professional or military design. IEDs by definition are "improvised" in some way, that is,
not a standard military or commercially designed explosive (although an IED could be improvised from one).
"Home made" explosives generally mean IEDs constructed solely from readily available materials, like bleach (hydrogen peroxide), fertilizers (ammonium nitrate), etc. -- whether or not they were actually made at any home.
So all "home made explosives" are IEDs, but not vice versa.
It's not clear from reports what kind of materials were seized in the Sydney raids.
I would guess they were widely available materials. From an aviation perspective, the good news is that most of these materials are detectable by security screening devices.