Same versions, different interfaces?

Each manufacturer can choose to put their own interfaces and tweaks to the phones they make. Manufacturers do this for various reasons. Some of the reasons is to differentiate their phones from other Android manufacturer's phones and to push selected services (their own or business partners') to the user of their phone. Some of the additions can be perceived as added value features. Some can be perceived as unwanted bloat ware. Sometimes, certain features are restricted as requested by carriers.

It is possible to remove this interface and use the default one, but it generally requires more knowledge than a basic user has.

 

There are rooting subforums and guides all over the internet. Yes, it does void your warranty. However, it's a software change (i.e not permanent). You can revert to stock should a warranty claim be necessary. Your call if it's worth it or not.

Just to clarify to the OP: this was the intent behind Android.