Working with CS5.5 fully patched, Word 2011 (14.1.0) on OS 10.6.8. When I import Word files in an InDesign CS5.5 document, some bold text remains bold, but some other turns into regular. Import options are OK.
Saving the word file as .docx or .doc doen't change anything. No problem with italic
Unfortunately, those Word files come from different users and asking them to use styles or even true bold and true italics is not an option...
Check your Word Import settings. Possibly the bold is assigned with a paragraph style in Word, and you have InDesign set to ignore paragraph style settings and honour local styling only (which would explain why your italics do come through).
There is no style in the Word document.