It's helpful to understand a little bit of how a PDF file works. A PDF file stores a sequence of instructions for what do draw on a page. The instructions are commands, such as "write this text here" or "draw a circle there." When you draw black redaction boxes, you are just appending an instruction to the end of the list ("draw a box here"), but most of the time the previous instructions are all still there. Really,…
Mrs Browl works at a e-discovery company where documents are often redacted depending on which bits are admissible in court; I gather they use TIFF files for exactly the reasons you describe. I suppose the (extremely limited) redaction features in Acrobat stem from the belief that the document is ultimately destined for printing rather than computer reading.
Here is an example of the process to apply redactions to a PDF file (or any sort of electronic document). The document is opened in a third-party native viewer with redaction capabilities (and not in the original application like Arcobat or Office). The end-user draws a black box over the appropriate text using the third-party native viewer. This redaction is saved as a separate layer that can be rendered on top of the native document when viewed in the software, as well as printed out. Finally, when documents need to be produced for court, they are printed out to a TIFF-printer driver, effectively converting them to TIFF and "burning in" the redaction layer. The TIFFs are delivered to the courts and opposing council.