Most of the time, I agree a shake is a shake (as long as you're talking vanilla/chocolate/strawberry and not one with add-ins like Reese's or Oreo chunks) but I had a strawberry shake at In-N-Out last year and it was literally the best "standard" shake I've ever had.
My wife would agree with your assessment of the in and out strawberry shake. Their fries, however fresh they may be, are garbage. Single cheeseburger, animal style, is great though. You have to eat it immediately because the bun fails fast.