In a regular AGO web map, when you edit a date field you see the date picker with 'today' automatically highlighted. If you edit a date field using the Edit or Smart Editor widgets in a web app, 'today' is not highlighted. The image below uses the same dataset.
This lack of consistency is annoying and having 'today' highlighted would help users quickly find and select 'today' - which is usually the most common date to enter.
UPDATE (05MAR2020): This only seems to apply when using the Dashboard Theme for Web App Builder.