They do send a lot of marketing emails but employ someone in-house to design those nowadays (who also handles the limited print ads that they still run).
Similarly, just offer clients retainer work. X amount per month, but you'll jump for them when needed. Example: we just had to get a designer to put something together for a really quick project. They were literally on call, turned it round in about 6 hours. Some months that's how it goes - a lot of work for not much. But other months they may not get a call.
This is not really true. Depending on the stack / type of project, there is a number of things you do on regular basis to maintain a project. People are bad at technology and a lot of it for me is usually fixing human error (especially CMS driven projects).
Also, the one time something breaks and the developer has to spend time rectifying the issue is spread out as a cost across a number of payments.
Not just a rant - there is an answer in what I've said - value is offered as part of the retainer. Client receives the peace of mind they need and doesn't have to worry about having to find someone to fight fires, when they do eventually hit.
Find things that offer value, be it peace of mind or something else, and upsell towards the end of your projects.
I deal with other servers, but leave these biggees to the full-time pros.
Good luck.