The first thing I want to say to you is based on what you describe here you seem to be a Gallant Asthmatic like Jake Gallant, and a true role model for other asthmatics.  I'm very impressed that you called your physician as soon as you observed your early warning signs so your asthma could be treated right away to prevent it from getting worse. 

To answer your question, not all asthmatics wheeze during asthma attacks, which is why it is essentially important that you follow your Asthma Action Plan, of which you did.  Even while your peak flows barely decreased, and you did not wheeze, your body gave you other signs that it was time to call your physician.

Likewise, it can be normal to not wheeze during an asthma attack, which can also be a sign of worsening asthma.  Often times when I give bronchodilator breathing treatments to an asthmatic in the hospital I hear more wheezes after the treatments than before, in which case wheezes can be a sign that your air passages are opening up and air is flowing more freely through them. So, for you, wheezing may be a sign that your asthma is improving.

Monitoring peak flows is a great way for most asthmatics to monitor their asthma, but for some reason peak flows do not drop for some asthmatics.  This is all the more reason for you to be aware of YOUR other early warning signs and to work with your doctor on creating an Asthma Action Plan that works best for you.  It appears you have one and followed it to a tee.  Great job.