So much this -- and it applies not only to bookstores but to retail in general. So many times I've thought "I should give these retail shops some support"; I go looking for something particular I want, spend several hours of my own time only to come up empty-handed because nobody had what I wanted in stock. Example: I read about some really cool Etymotic musician's earplugs. I thought great, there's actually an instrument store near my work. Walked there; nope, none in stock. Or reading about one of those induction cooktops. Went to my local big-box electronics/appliances retailer. Nope, nothing. Pretty much anything that's even slightly niche, it seems like retail just doesn't have it.
As for books in particular - Kindle wins hands-down on convenience and portability for me, over bookstores (the 'walk-out' part is definitely covered). In my particular case, as I'm vision-impaired, Kindle ALSO wins hands-down on usability, because I can make the text any size I want. That's important enough for me that it can mean the difference between actually being able to read a book and not being able to read it.
I think I have 451 Kindle books. I can carry all of those in my pocket on my phone or in my backpack on my tablet, if I want. That's another huge advantage.
I should probably mention that given all that, I _still_ like physical books! I remember walking the aisles of Borders, but that was because they were huge and they had books in the niche I was looking for. I fondly remember a small bookstore that used to specialise in software development and IT books and they had a great selection of game development books. I used to love that place! For me though, that was all before I got a taste of the convenience of Kindle. Getting the book is worth more to me than stopping and having a nice coffee at the bookstore.