Here is a response I got from Empower early this morning. Since I downloaded v72, I must need the v80 they mention:
Thank you for writing to us. The compatibility of Empower Pro on OS 4.5 depends on the exact version of OS 4.5. Unlike older OSes like 4.1, 4.2 and 4.3 etc, in OS 4.5 there are two sections. While Empower Pro works perfectly on OS v220.127.116.11 and v18.104.22.168 there are some versions like v22.214.171.124 and v126.96.36.199 which do not allow Empower Pro to access emails with attachments.
So, depending on which exact OS 4.5 version you upgrade to - you will need either Empower Pro v.72 or v.80.
While it is true that OS 4.5 has its own native html-view, there are a number of reasons why people continue to use Empower Pro on OS 4.5 and even on Bold. One is that Empower Pro formats better, is more sleek and has features like auto-downloading of images and Image Cache, Add To Task and Add to Calendar etc. which are not available in the native viewer.
Thanks & Regards,
Team Empower, Empower BlackBerry HTML Email Viewer