Small question about romanizing long vowels

[BigBoss4]

Just a small question, why is it that in some japanese media/texts they sometimes omit the final vowel of lengthened vowels?

e.g.
Kyuu (キュウ/キュー) becomes kyu, or Ryuuga (龍牙) becomes Ryuga (without the macrons/circumflexes)
I've tried searching for similar topics (and on the net) but they keep referring to using Hepburn romanization.

 

[Red5]

I think when you use hiragana style , you can add for the vowel another sound to be come long like ,
(キュ here you can this ウ)

but in katakana , you've to add ー to make the vowel long .

 

[Toritoribe]

Just a small question, why is it that in some japanese media/texts they sometimes omit the final vowel of lengthened vowels?

e.g.
Kyuu (キュウ/キュー) becomes kyu, or Ryuuga (龍牙) becomes Ryuga (without the macrons/circumflexes)
I've tried searching for similar topics (and on the net) but they keep referring to using Hepburn romanization.

Wiki has the explanation.

Romanization of Japanese - Wikipedia