This made me think I was reading a necro thread from 2005. Those arguments would make sense then.
Have you stepped outside in a while? Unless you're buying a $3,000 Alienware laptop, this all applies today. Just doing a general search at Newegg, there's only 34 gaming laptops listed with 18" screens and a whopping
one laptop with a 21" screen. If you really want to try for that 21" screen laptop, you'll be spending $8,999.00 (on sale from $8,999.99!). If you don't care about a 21" screen and just want the smaller 18", you'll still be dropping over two grand for a mid-range one.
No, all of what he said still applies today. If you want mobility, you'll be getting weaker hardware for more money. If you want mobility and power, you'll be pulling a second mortgage on your house.
I understand the appeal of wanting to move your gaming session around the house or maybe just relax on the bed/couch and keep gaming, but you still can't spec a laptop the same as a desktop and expect the prices to remain equal.