On the PBS site it states ""If you use metered postage (purchased from the PO counter or from an Automated Postal Center), you do not have to hand your package to a postal employee."

My question is if I use a metered postage sticker from my postage machine at work, is it OK to drop the package in a blue mailbox?

Dorothy, yes, you may use a postage machine metered sticker from work and drop it off in the blue box regardless of the weight.  I buy all of my postage from my office, the accounting guy hates it because it requires him to reconcile the petty cash box, but it is so convenient.  With a APC postage meter label, you do not need to use it immediately because the date on it shows the date of purchase.  Using a work postage meter, you need to make sure the date on the label is the current day's date.  Otherwise it is considered stale mail and you'll need to put a 00 label on it with the current date. 

Even under the old limit of 1 lb. you could use your meter.  The PO is looking at traceable postage vs non-traceable.  Actual postage stamps are not traceable.