While true, it's often two distinct processes. I work with implementing ERP systems, focusing on accounting and financials. Most systems I see use the ERP system to generate the invoice data and for tracking the invoice status with a separate service to create the PDF (and electronic) invoices through an integration with the ERP system. The ERP system is usually pretty good at invoice tracking but customising the invoices can be both time consuming and expensive. Among larger enterprises there's definitely a market for software that can produce PDF invoices, even without tracking, although they would probably have to support creating PEPPOL BIS compliant XML documents as well.
I could be wrong, but if the business is using ERPs (to the extent of hiring implementation specialists), they're likely already too big for this type of software. In it's current form anyways, this feels like something small business uses to appear professional, big and/or well polished. The bigger company would use the ERP solution because it integrates with their general ledger, etc. and at that scale putting any focus on 'pretty invoices' is probably just a waste of time. It's really better to focus on getting them paid quickly.
