[big soft moose]

So i'm building a top bar hive... all the american plans I've seen have landing platforms, but the British ones don't - also the american ones have slot entrances while the British ones have holes.

Is there a sound reason for this either way, or is it just a cultural thing ?

[cloddopper]

 Top bar ..... long hives triangular in shape
If so .... My mentor Alvin gave me the following advice .. by way of a question .. Do feral nests in hollow trees  have them ? He then went on to say birds cannot land on them if they aren't there . Same applies to wasps & hornets . Not having a  board  helps the hive defend itself  . It's easier to pin a mouse guard over the entrance if there is no board .

 Re:-  The holes .. 
 I've only see one , sometimes two , 3/4 " dia drilled entry holes near the bottom of the V shape on one end panel only . Alvin used to have a fine insect mesh nylon screen  pinned with thumb tacks across the bars so they didn't all fly up at him as he took the lid off to smoke them .
Once smoked to being really quiet he undid the pins at the rear of the long hive & rolled the screen forward top the front to gain access to the filled natural comb .

 I'd think that slots might give the bees draughts

 If it is Lanstroth commercial type hives with a top bee space you are meaning , made up of a brood box & several supers .    Sit the hive on a base board so that you have a 3/4 side wall above the floor to sit the brood box on ... again there is no need for landing boards  unless you like wasting wood .

Do make up a strip of wood slightly wedge shaped  with one or two bee space cut out's in it so you can close up the entrances by pushing in the block during the hive robbing season . The bees will find it much easier to defend the two smaller cut out entrances than the whole width of the floor board  .
If there is a nectar flow on during hot humid periods , take the bar out to allow the bees maximum gathering of nectar & pollen with minimum effort to get the maximum amount of honey .
 

[Birchlea]

I'm a beginner but a local expert has told me that bees don't need landing boards. They can happily come and go without them but keepers like them as they can observe bees more easily as they land and walk in.
It appears to be the keepers choice. I have landing boards and enjoy watching the bees gather on them!

[NewToThis]

They're quite happy without - but I have them as I find it allows be to observe the bees coming and going and gives me an indication of how the hive is doing between inspections