Since Kobo is using mobile Adobe Digital Editions as its reading engine, it is surprising that it does not support reflow (which is a standard option for mobile ADE). The only other ADE licensees that I am aware of that do not support PDF reflow are Amazon (Kindle) and Bookeen (e.g. Cybook Gen3). The best implementations of ADE PDF (e.g. PocketBook) support both reflow and zooming (with many more zoom options than Kobo).
I have updated the E-book Reader Matrix
for Kobo, but the "PDF Capabilities" column may be incomplete (compare it to the Cybook column). Does the Kobo handle PDF TOC's and/or hyperlinks within the PDF for example? How about cropping the margins of PDFs? In general, feel free to update the Kobo column of the Matrix, or reply here and I'll do it.