For a start:
'pop' just means popular. Popular music isn't style-specific - it is simply the music that the majority of a specific demographic listen to.
If you go to Ibiza, dance music is pop. If you go to Poland/Eastern Europe, Heavy rock/Metal is pop.
There is no such thing as purely 'pop' music. Bullet For My Valentine are pop, but they aren't just pop.
RE Rap/Hip Hop music: this music is perfect as specific to the tempo of the music. Generally, as far as club music goes, the faster the tempo, the straighter the rhythm. You have to remember that the purpose of hip-hop/dance etc is that it is designed for dancing to. As examples of music to dance to, they are pretty spot on. Therefore, you can't say it is lacking in musical value.
RE 'proper' music - hip-hop music has very complex bass drum patterns, which are directly connected to the tempo of the music. Try working out the bass drum rhythm to music by, for example, MIMS.
Rap/Hip Hop is actually very complex. As a starter - dance music above 130 bpm - bass drum rhythm = pure crotchets ('four on the floor' e.g. Cascada). Dance music between 80 - 130 bpm - bass drum has quaver patterns (e.g. T-Pain); dance music under 80/90 bpm - bass drum has many semiquaver rhythms.
Most people comment on rap being unmusical or 'not true music' when the simple fact is they don't understand it, or have never studied it. Some of the most difficult, syncopated rhythms can be found in rap music.
And if you consider sampling to be unmusical, then just listen to Aoki Takamasa, or I am Robot and Proud.
Or Aphex Twin.
PS before you think i'm anti-rock music, i'm a guitarist. I'm just not an ignorant guitarist.
You'll probably find that most professional musicians aren't dismissive of any style of music, as they all know that good music, no matter what style, requires effort and originality.