All organisms have ribosomes in most of their cells

Statement

All organisms have ribosomes in most of their cells.

One known exception is mature red blood cells in mammals; these also lack a mitochondrion or nucleus.

Justification for presence in most cells of all organisms

Ribosomes are necessary for protein production, part of the central dogma of molecular biology

The central dogma of molecular biology says that DNA makes RNA, and RNA makes protein. Ribosomes are what executes the "RNA makes protein" step. Protein production is central for life, so all organisms need ribosomes.

For any cells that are not terminal, i.e., they have plans to divide further, protein production is necessary locally within the cell in order for each of the daughter cells to have proteins. Thus, the only potential exceptions would be mature cells that don't need to divide further and have already made enough protein for their internal needs.