No, Windows x86-32 will only use up to 3.25 GB of RAM. Up to 4 GB is just a generalization.32-bit supports up to 4GB of RAM. That 0.8GB RAM that's inaccessible in your example has to do with video memory, etc. 32-bit still supports up to 4GB of RAM natively.
To be accurate, 32-bit can use more RAM (up to 64 GB in some OSes), but Microsoft intentionally limited it to 3.25 GB.