Buyers who account for the majority of revenue for a given product are normally offered preferential treatment of some sort. This would seem fair, but to the surprise of many online professionals this is often not the case when it comes to software vendors or digital agencies.
Over the years I've talked to practitioners around the world from large and complex organisations who have been genuinely disappointed by how they have been treated by their vendors. Despite having been big spenders on licenses or in terms of consulting hours (or both), they still feel that the vendor is not listening to requirements and paying any real attention to their needs.
A good example is how Microsoft have treated their CMS customers in the past. The early adopters were left behind with Microsoft CMS 2002 without an upgrade option when Microsoft released SharePoint 2007. Large organisations, such as drinks giant Carlsberg, global manufacturer Danfoss and Royal Mail in the UK, did adopt CMS 2002 yet still Microsoft decided that it was best to ask customers to start all over again.
For smaller vendors, there are several worse examples of poor key account management that have left customers frustrated.
My usual advice is that it helps talking to vendors. It helps even more if you join up with other buyers. Even if you don't work in a large multinational or for a world-famous NGO, you can become a key account by using diplomatic skills and engaging in a dialogue with your vendors, so that your projects are visible inside the vendor organisation.
The real definition of a key account is not necessarily tied to revenue. You are a key account if the vendor listens to you, accepts your feedback, specifies appropriate actions and shares a timeline with you. You need to be patient, you need to be forgiving, you need to be reasonable, but the rewards in potential cost savings and ability to plan better should make it well worth it.