e-Books versus print books

I was getting disheartened by the lack of notifications from Amazon of sales of any of my books. I still make sales myself to those unfortunates who are seated next to me on plane rides and are thus victims to the sales pitch, but as plane rides are few and far between these days, I will not get rich doing that. However, I have been pleasantly surprised by notices from Amazon Accounts Payable of monies posted to my acount. I admit the sums are not vast and as they say I should definitely not give up my day job, whatever that is, but it is welcome money all the same. The receipts come from e-Book sales and, surprisingly to me, the book that sells the best is "Just off the Great North Road". Quite why that is is a mystery to me, perhaps the title, perhaps the cover image. What it does confirm for me is that any new releases need to go out as an e-Book at the same time as the print version, or perhaps I'll try one that is e-Book only with no attendant print version.