My LO is the same and is actually 1 on Sunday so I know how you mean.
She wont stand on her own either and will sometimes topple over when she is cruising. She would love to walk though - but I think she's a bit nervous to fall flat on her face on the laminate flooring to be honest.
But she gets herself to her knees and will pull herself up on your legs.
I wouldn't worry about it. If by 18 months he isn't walking at least a few steps I would go to your health visitor or doctor and mention it. Some babies are late learners to walk.
I think personally it's because they are focusing on other areas of development. Is he a good speaker/good with his hands?
My daughter is very tactile with her hands and has a pincher grip since about 7/8 months old. She also picks minute bits up off the floor and flicks them as well as hurling things across the other side of the room.
She also has 6 noticeable words that we can understand and a few others we aren't sure what they are but she says them regularly, so they must mean something. I feel she's just focusing on her hand eye co-ordination and her speech more than her walking.
I pretty much took my first steps on my first birthday but I could stand on my own for about a month before then, or so my mother says.
She's also got 4(maybe 5) teeth whereas I had only 3 on the day of my first birthday so I think it could depend a lot on what other things are going on in babies life too. Especially if they've had a cold/flu etc around a big developmental leap.
I'm sure he'll start walking in no time though. I'm enjoying it for the time being because when my daughter starts to walk, she'll be a little terror!