Yes, this is something that happens in day to day casual conversations a lot. The elimination of the 'w' sound is most common with 'ㅂ', and 'ㅁ', sound that use the lips. For example, 봐 - is said a lot of the time as [바], but you cannot say 와 as [아] another example is '뭐', as it can be said as [머] . as for the other, 왜, 돼, these will be said with the 'w' sound. 위, 귀, 뒤 - these will also be said with the 'w' sound.

It is not a standard pronunciation. The standard pronunciation of ㅟ [ y ] single vowel sound. Nowadays, It often pronounced as [ wi ] in the initial of word, [ ʷi ] in the middle of word. I guess you heard Gyeongsang(Southeastern Korean) dialects. Most Gyeongsang dialects have six vowels, a (ㅏ), e (ㅔ), eo (ㅓ), o (ㅗ), u (ㅜ), i (ㅣ). In most areas, the vowels ㅐ(ae) and ㅔ (e) are conflated, as are ㅡ(eu) and ㅓ(eo). W and y are generally dropped after a consonant, especially in South Gyeongsang dialects. For example, soegogi (쇠고기) 'beef' is pronounced 소고기sogogi, and gwaja (과자) 'sweets' is pronounced 가자gaja. Vowel harmony differs from the standard language. For instance, oneul (오늘), meaning "today," is pronounced 오날onal. The main difference is that e is considered a central vowel. Vowels are fronted when the following syllable has a y or i, unless a coronal consonant intervenes. For example, 어미eomi 'mother' is 에미emi, and 고기gogi 'meat' is 게기gegi.